Re-Evaluating Split-Fovea Processing in Word Recognition: Effects of ...

Neuropsychology 2008, Vol. 22, No. 6, 738 –745

Copyright 2008 by the American Psychological Association 0894-4105/08/$12.00 DOI:10.1037/a0013140

Re-Evaluating Split-Fovea Processing in Word Recognition: Effects of Retinal Eccentricity on Hemispheric Dominance Timothy R. Jordan, Kevin B. Paterson, and Marcin Stachurski University of Leicester Several studies have claimed that hemispheric asymmetries affect word recognition right up to the point of fixation because each fovea is split precisely at its vertical midline and information presented either side of this midline projects unilaterally to different, contralateral hemispheres. To investigate this claim, four-letter words were presented to the left or right of fixation, either close to fixation entirely in foveal vision (0.15, 0.25, and 0.35 degrees from fixation) or further from fixation entirely in extrafoveal vision (2.00, 2.10, and 2.20 degrees from fixation). Fixation location and stimulus presentation were controlled using an eye-tracker linked to a fixation-contingent display and performance was assessed using a forced-choice task to suppress confounding effects of guesswork. A left hemisphere advantage was observed for words presented in extrafoveal locations but no hemisphere advantage (left or right) was observed for words presented in any foveal location. These findings support the well-established view that words encountered outside foveal vision project to different, contralateral hemispheres but indicate that this division for word recognition occurs only outside the fovea and provide no support for the claim that a functional split in hemispheric processing exists at the point of fixation. Keywords: word recognition, laterality, hemispheric asymmetry, visual fields, split fovea

(bilaterally) to both the LH and the RH (for relevant reviews, findings, and opinions, see Brandt, Stephan, Bense, Yousry, & Dieterich, 2000; Bunt & Minckler, 1977; Fendrich, Wessinger, & Gazzaniga, 1996; Gazzaniga, 2000; Leventhal, Ault, & Vitek, 1988; Lindell & Nicholls, 2003; Reinhard & TrauzettellKlosinski, 2003; Stone, 1966; Stone, Leicester, & Sherman, 1973; Trauzettell-Klosinski & Reinhard, 1998). Indeed, researchers investigating hemispheric asymmetries in word recognition often present stimuli at least 2 degrees to the left or right of a central fixation point to ensure that these stimuli are presented at eccentricities that are safely beyond the boundary of bilateral projection, and so project unilaterally to either the LH or RH (for a recent review, see Lindell & Nichols, 2003). In recent years, however, some researchers have promoted the contrasting view that hemispheric asymmetries affect word recognition right up to the point of fixation because each fovea is divided precisely at its vertical midline and all information either side of this midline projects (unilaterally) to the contralateral hemisphere (for reviews, see Jordan & Paterson, 2008; Lavidor & Walsh, 2004; Lindell & Nicholls, 2003). Thus, according to this “split-fovea theory” of word recognition (hereafter SFT), all information presented to the left of fixation will project to the RH, and all information presented to the right of fixation will project to the LH, and this division in hemispheric processing at the point of fixation produces substantial effects on word recognition (e.g., Shillcock, Ellison, & Monaghan, 2000; Shillcock & McDonald, 2005). Although advocates of SFT argue that the theory is supported by anatomical evidence (e.g., Leff, 2004), the issue is far from resolved (e.g., Brandt et al., 2000; Bunt & Minckler, 1977; Fendrich et al., 1996; Gazzaniga, 2000; Leventhal et al., 1988; Lindell & Nicholls, 2003; Reinhard & Trauzettell-Klosinski, 2003; Stone, 1966; Stone et al., 1973; Trauzettell-Klosinski & Reinhard, 1998; for a critical review, see Jordan & Paterson, 2008). Consequently, SFT researchers have also attempted to reveal functional evidence

For many years (e.g., Mishkin & Forgays, 1952), research using lateralized visual displays has shown that words are processed more efficiently when presented in the right visual hemifield (and so project directly to an observer’s left hemisphere, LH) than when presented in the left visual hemifield (and so project directly to an observer’s right hemisphere, RH; for overviews, see Bradshaw & Nettleton, 1983; Chiarello, 1988; Hellige, 1993). The precise nature of the processes that underlie the perception of words in each hemisphere and that are responsible for this effect is widely debated (e.g., Bub & Lewine, 1988; Burgund & Marsolek, 1997; Ellis, 2004; Ellis, Young, & Anderson, 1988; Jordan & Patching, 2003a, 2003b; Jordan, Patching, & Milner, 1998, 2000; Jordan, Patching, & Thomas, 2003a, 2003b; Jordan, Redwood, & Patching, 2003; Lavidor, Babkoff, & Faust, 2001; Reuter-Lorenz & Baynes, 1992). Nevertheless, there seems little doubt that the advantage for words projected to the LH reflects privileged access to specialized LH processing of linguistic information. Although evidence for the projection of information in each hemifield to the contralateral hemisphere is well-established, the projection of information around the point of fixation has become a matter of debate in word recognition research. At the origin of this debate is the widely accepted view that a sizable area of overlap (typically regarded as 1–3 degrees wide) exists around the point of fixation within which information projects

Timothy R. Jordan, Kevin B. Paterson, and Marcin Stachurski, School of Psychology, Faculty of Medicine and Biological Sciences, University of Leicester. This research was supported by the Wellcome Trust (Grant no. 059727) and the Ulverscroft Foundation. Correspondence concerning this article should be addressed to Timothy Jordan, School of Psychology, Faculty of Medicine and Biological Sciences, Henry Wellcome Building, University of Leicester, Leicester LE1 9HN, United Kingdom. E-mail: [email protected] 738

RE-EVALUATING SPLIT-FOVEA PROCESSING IN WORD RECOGNITION

of split-foveal processing by directly observing the influence on word recognition of presenting stimulus information at different eccentricities around the point of fixation. A study by Lavidor, Ellis, Shillcock, and Bland (2001; see also Skarratt & Lavidor, 2006) is representative of this approach and is often cited as support for SFT. This study draws on earlier findings that, it has been argued, indicate that increasing the number of letters in words affects RH processing but not LH processing (e.g., Ellis et al., 1988; Young & Ellis, 1985; although see Jordan et al., 2000, 2003a). Accordingly, Lavidor et al. presented words at different eccentricities so that the majority of letters were projected to either the left (yea|rn, lovelo|rn) or right (ex|cel, ex|orcise) of a central fixation point (designated here by |). In this way, word displays were designed to project a variable number of letters (3 or 6) to either the left or right of each participant’s point of fixation and, if SFT is correct, the same variable number of letters to the RH and LH, respectively. Lavidor et al. reported that increasing the number of letters impaired performance only when this increase occurred to the left of the fixation point (i.e., yea|rn, lovelo|rn). Thus, according to the logic of this study, letters to the left of fixation projected to the RH (because number of letters affected word recognition) and letters to the right of fixation projected to the LH (because number of letters did not affect word recognition) and this provides evidence of split-foveal processing. Similar approaches have been taken by other studies that report findings that are interpreted as support for SFT (e.g., Brysbaert, 1994; Brysbaert, Vitu, & Schroyens, 1996; Hunter, Brysbaert, & Knecht, 2007; Martin, Thierry, De´monet, Roberts, & Nazir, 2007; see also, Brysbaert, 2004). For example, Brysbaert et al. (1996) investigated recognition of words presented at various eccentricities around a central fixation point. Across the experiment, words were offset to the left or right of the fixation point so that they either straddled the point at various locations or were shown entirely to the left or right in nearby locations (0.67 or 1.33 degrees away from the fixation point). The findings showed a word recognition advantage when most of the letters in a word, or words in their entirety, were shown to the right of the fixation point. Thus, according to the logic of this study, word recognition was determined by the hemisphere to which the letters presented to the left and right of fixation were projected, and a processing advantage was produced when most or all of these letters were presented to the right of the fixation point because (and in line with SFT) these letters projected to the LH. Brysbaert (1994) and Hunter et al. (2007) have used a similar technique with participants who were either LH dominant for language processing or from a small percentage of people who are RH dominant. The findings from both studies showed a word recognition advantage when most or all of the letters in a word were shown to the right of the fixation point but only for participants with typical (i.e., LH dominant) hemispheric lateralization. Consequently, according to the logic of Brysbaert (1994) and Hunter et al. (2007), word recognition was also determined by the dominance of the hemisphere to which letters to the left and right of fixation were projected. For LH-dominant participants, projecting most or all letters to the LH produced a processing advantage that was unavailable to RH-dominant participants. Martin et al. (2007; see also Martin, Nazir, Thierry, Paulignan, & De´monet, 2006) also examined performance with words that straddled a central fixation point at various locations. Although Martin et al.

739

focused on the electroencephalographic activity of their participants and do not report fully the effects of fixation location on word performance, they argue that the effects of fixation location on word recognition performance they observed are consistent with those of Hunter at al. and, accordingly, support SFT. The logic behind all of these studies (Brysbaert, 1994; Brysbaert et al., 1996; Hunter et al., 2007; Lavidor et al., 2001; Martin et al., 2007; see also, Brysbaert, 2004; Ellis, 2004) is that if word recognition is affected by unilateral, contralateral hemispheric projections that occur right up to the point of fixation (as SFT proposes), this division in processing will be revealed by hemispheric asymmetries in performance even when information is presented within foveal vision close to fixation. However, this logic rests on the assumption that participants in these studies fixated the designated fixation point with sufficient accuracy to ensure that information presented either side of this point projected to the appropriate hemisphere. Unfortunately, it is well-established that participants have great difficulty monitoring and controlling their eye movements when attempting to fixate a specified location and accurate fixation cannot be ensured without external monitoring and control (i.e., by using an eye-tracking device; for reviews, see Gazzaniga, 2000; Jordan et al., 1998, 2000; see also Anliker, 1977; Batt, Underwood, & Bryden, 1995; Findlay & Kapoula, 1992; Jones & Santi, 1978; Jordan & Patching, 2006; Jordan et al., 2003a, 2003b; Jordan, Paterson, & Stachurski, 2008; Patching & Jordan, 1998; Sugishita, Hamilton, Sakuma, & Hemmi, 1994; Terrace, 1959). Indeed, several studies indicate that systematic fixational biases can occur to the left or right of the required fixation location and that although these biases are likely to affect word recognition they are unlikely to be detected if an eye-tracking device is not used (e.g., Findlay & Kapoula, 1992; Jones & Santi, 1978; Jordan et al., 1998; Jordan & Patching, 2006; Jordan, Patching, & Thomas, 2003; Terrace, 1959). However, participants in the studies by Brysbaert (1994); Brysbaert et al. (1996); Hunter et al. (2007); Lavidor et al. (2001), and Martin et al. (2007) were simply instructed to fixate the designated fixation location in each experiment (sometimes accompanied by a secondary fixation task) with no external monitoring or control to determine which locations were actually fixated.1 As an indication of the problem, Jordan et al. (2008) used the same stimuli, displays and procedures as the study by Lavidor et al. (2001) in which words were offset to the left or right of fixation (yea|rn, lovelo|rn, ex|cel, ex|orcise), but also an eye-tracker that showed the locations of fixations actually made by participants. The findings revealed that participants failed to fixate the designated location on approximately 50% of trials, and inaccurate fixations fell at least 0.25 degrees (over two letters) and up to 1 degree (more than the width of a complete word) away (Jordan et al., 2008). The frequency and extent of these inaccurate fixations cast considerable doubt on the notion that, without external mon1 Recent evidence has revealed that instructions to fixate a designated point do not ensure fixation accuracy even when combined with a secondary fixation task (e.g., identifying a digit presented at the required fixation location). In fact, when participants were instructed to fixate a fixation point, accurate fixation occurred on only 25% of trials and a secondary fixation task produced no significant improvement in this level of accuracy (Jordan, Paterson, Stachurski, Kurtev, & Xu, 2007).

740

JORDAN, PATERSON, AND STACHURSKI

itoring or control, stimuli presented around the point of fixation can be projected reliably to the required side of fixation and, therefore (if SFT is correct), to the appropriate hemisphere. Indeed, over the three experiments conducted in their study, Jordan et al. found no evidence to support the findings of Lavidor et al. or the proposals of SFT, and found instead that the effects of fixation location reflected the well documented and long established optimal viewing position for word recognition (e.g., O’Regan, 1981; for a recent review, see Jordan et al., 2008). The problem of accurately projecting foveal information to the appropriate hemisphere in previous studies supporting SFT is further complicated by the use of stimuli that exceeded the area of foveal vision. In particular, since the notion that unilateral contralateral projections exist outside foveal vision is well-established and not contentious (for a review, see Gazzaniga, 2000), support for the view that unilateral contralateral projections affect word recognition right up to the point of fixation (i.e., SFT) would be more convincing if stimuli presented about the point of fixation did not extend into extrafoveal locations. Lavidor et al. (2001) report using stimuli that could fit entirely within the area that is generally assumed to correspond to foveal vision (up to 1.5 degrees either side of fixation). However, the approach taken by Brysbaert (1994); Brysbaert et al. (1996); Hunter et al. (2007), and Martin et al. (2007) was less appropriate. Brysbaert (1994) presented stimuli of 3, 4, 5, 7, and 9 letters in length but only stimuli of three and four letters were sufficiently physically small to always be shown entirely within foveal vision (notwithstanding the problems of fixation accuracy already described). For all other lengths, stimuli frequently exceeded the area of foveal vision (by up to 1.5 degrees), making it unclear how effects of presenting stimuli to the left and right of the designated fixation point reflected the influence of unilateral projections in foveal, not extrafoveal, vision. Similarly, Brysbaert et al. (1996) used stimuli of 3, 5, and 7 letters but, in line with the study by Brysbaert (1994), only three-letter stimuli were sufficiently physically small to always be shown entirely within foveal vision and all other stimuli would have frequently exceeded this area. Hunter et al. (2007) do not report the physical size of the stimuli used in their study and so provide no indication of the extent to which stimuli were presented in foveal and extrafoveal locations. However, the study is reported as a replication of Brysbaert’s (1994) study using different methods of determining hemispheric asymmetry, so the indication is that similar problems of disentangling foveal and extrafoveal projections existed. Finally, the five-letter stimuli used by Martin et al. (2007) subtended a horizontal visual angle of 6.65 degrees (five letters would subtend about 1.25 degrees in normal reading; e.g., Rayner & Pollatsek, 1989) so more than 75% of each stimulus would have been presented in extrafoveal locations when either the first or last letter was fixated. Moreover, such was the physical size of these stimuli that when any other letter position (2– 4) was fixated, stimulus information would have been presented in extrafoveal locations on both sides of the fixation point. The situation is further complicated by disparities that frequently occur between the locations fixated by each eye (e.g., Blythe, Liversedge, Joseph, White, Findlay, & Rayner, 2006; Fioravanti, Inchingolo, Pensiero, & Spanios, 1995; Juhasz, Liversedge, White, & Rayner, 2006; Liversedge, White, & Rayner, 2006; Liversedge, Rayner, White, Findlay, & McSorley, 2006; for a review, see Kirkby, Webster, Blythe, & Liversedge, 2008).

Specifically, when fixating, two locations may often be fixated, one by each eye, and so the information falling on either side of the foveal midline may often differ between the two eyes. Binocular disparity has not been a focus in previous investigations of hemispheric asymmetries in foveal word recognition (e.g., Brysbaert, 1994, 2004; Brysbaert et al., 1996; Ellis, 2004; Hunter et al., 2007; Lavidor & Bailey, 2005; Lavidor et al., 2001; Lavidor, Ellison, & Walsh, 2003; Lavidor & Walsh, 2004; Martin et al., 2007; Shillcock et al., 2000; Shillcock & McDonald, 2005; Skarratt & Lavidor, 2006) but such disparities clearly have the potential to contaminate assessments of SFT. Accordingly, the present research reevaluated the fundamental claim of SFT that a division in hemispheric processing at the point of fixation plays a functional role in word recognition. To investigate this claim, words were presented to the left or right of fixation at eccentricities that placed them either close to fixation entirely in foveal locations (with medial edges 0.15, 0.25, and 0.35 degrees from fixation) or away from fixation entirely in extrafoveal locations (with medial edges 2.0, 2.10, and 2.20 degrees from fixation). An eye-tracking system linked to a computer-controlled, fixation-contingent display ensured accurate fixation when each word was presented, and monocular presentations via each participant’s dominant eye avoided fixational aberrations produced by binocular fixation disparity. All participants were selected to be LH-dominant for language and all had previously shown the well-established LH advantage for words presented in extrafoveal locations. The predictions of the experiment were clear-cut. If SFT is correct in proposing that unilateral projections to each contralateral hemisphere influence the recognition of words in all locations up to the point of fixation, words presented to the right of fixation should produce LH advantages not only when presented in extrafoveal locations but also when presented close to fixation, in foveal locations. If SFT is not correct, however, and unilateral foveal projections to each contralateral hemisphere do not influence word recognition, only words presented in extrafoveal locations should produce a LH advantage and words in foveal locations should produce similar levels of performance on each side of fixation.

Experiment Method Participants. Sixteen native English speakers (nine males, seven females) aged 18 to 35 from the University of Leicester were paid for participating. All participants had at least normal (or corrected to normal) acuity, determined by a Bailey-Lovie Eye Chart, and were right-handed, determined by a score of 100% on a revised Annett Handedness Questionnaire (Annett, 1970). Eye dominance was determined individually for each participant using both the Miles test (Miles, 1930) and the Porta test (Porta, 1593; see also Crovitz & Zener, 1962; Gronwall & Sampson, 1971; Porac & Coren, 1976; Roth, Lora, & Heilman, 2002) of ocular dominance. All participants were right eye dominant. Stimuli. Following previous studies of hemispheric asymmetry, performance in each location was assessed using the ReicherWheeler task to provide an assessment of LH dominance for word recognition that is not contaminated by perceptual asymmetry and guesswork and which demonstrates processes of word perception (e.g., see Jordan et al., 1998, 2000, 2003; Reuter-Lorenz &

RE-EVALUATING SPLIT-FOVEA PROCESSING IN WORD RECOGNITION

Baynes, 1992).2 Accordingly, 64, four-letter words with a mean frequency of 87 per million (according to the CELEX database, Baayen, Piepenbrock, & Gulikers, 1995) were used in the experiment and an additional 12 words served as practice stimuli. Following the requirements of the Reicher-Wheeler task, words were selected to form matched pairs in which the members of each pair differed by just one letter (e.g., show, snow) and these differences occurred equally often at each of the four letter positions across all stimuli. Stimuli were presented in lower-case Arial font at three foveal and three extrafoveal locations to the left and right of a central fixation point. The physical size of stimuli presented at foveal and extrafoveal locations was adjusted to avoid confounding effects of acuity on overall levels of performance (e.g., Drasdo, 1977). Foveal stimuli subtended 0.55 degrees and the medial edge of these stimuli was 0.15, 0.25, or 0.35 degrees from the fixation point. Extrafoveal stimuli subtended 1.10 degrees and their medial edges were 2.00, 2.10, or 2.20 degrees from the fixation point. Preliminary testing had established that these sizes and eccentricities produced similar levels of overall performance for foveal and extrafoveal displays and also ensured that stimuli were shown entirely in either foveal or extrafoveal locations. Apparatus. Stimuli were presented on a gamma-corrected high-definition 21 in. ViewSonic G220F display monitor. A Cambridge Research Systems VSG 2/5 card controlled stimulus presentations and timing. Responses were collected via a Cambridge Research Systems CT3 button box. The experiment was conducted in a sound-attenuated and darkened room and displays were observed using a head restraint to ensure a constant viewing distance of 60 cm. Each participant’s nondominant eye was occluded using a light-proof eye-patch (Cambridge Research Systems) and the fixation location of the dominant eye was monitored using a Skalar IRIS eye-tracking system (Cambridge Research Systems). The eye tracker was clamped to each participant’s head, which in turn was clamped in a head brace throughout the experiment to prevent head movements. This arrangement allowed accurate and consistent measurement of fixation location in the experiment to within 5⬘ of arc (for further details, see Jordan & Patching, 2006; Patching & Jordan, 1998). The output of the tracker was recorded through the ADC input of the Cambridge Research Systems VSG 2/5 card, which also controlled the visual display (for further details, see Jordan et al., 1998, 2000). Design. Participants took part in four sessions, one on each of four different days. Within each session, words were selected pseudorandomly and assigned pseudorandomly to retinal locations so that 16 presentations took place at each retinal location in each session (a total of 192 presentations). Across all sessions, each word was shown once in each retinal location. Procedure. At the start of each trial, a single but clearly visible pixel (the fixation point) was presented at the center of the screen. Participants were required to fixate this point and word presentation was prevented until accurate fixation occurred continuously for 300 ms. When this criterion was satisfied, a word was presented for 16.67 ms at one of the 12 locations. If fixation deviated from the fixation point before the presentation of the word, word presentation was immediately prevented and continued to be prevented until accurate fixation occurred again for at least 300 ms (see Patching & Jordan, 1998, for further details of this procedure). No deviations in fixation occurred during the presentation of each word. The target word and its matched pair-mate were displayed

741

400 ms after each target presentation, one above the other, and participants decided which of these two words had been shown by pressing the upper or lower key on the response box. The alternatives were presented in a size intermediate between the two sizes used for target presentations (0.825 degrees) at the bottom of the screen well away from the locations at which targets were presented and stayed in view until a response was made. Half of the participants responded with their right hand and half with their left hand.

Results Mean identification accuracy for words presented at each of the 12 foveal and extrafoveal locations is shown in Figure 1. Overall levels of performance were closely matched for foveal (67%) and extrafoveal (68%) stimuli, indicating that the size manipulations used in the experiment successfully matched stimulus visibility across foveal and extrafoveal locations. A preliminary analysis of variance (ANOVA) was conducted with variables response hand, session, the hemisphere to which words were projected (LH, RH), retinal eccentricity (foveal, extrafoveal) and local eccentricity (inner, middle, outer). Local eccentricity refers to the three locations either side of fixation at which stimuli were presented foveally and extrafoveally: inner (nearest to fixation), middle, outer (furthest from fixation). The analysis showed no effect of response hand or session (all Fs ⬍ 1.4) but did show an interaction of hemisphere, retinal eccentricity, and local eccentricity, F(2, 30) ⫽ 5.95, p ⬍ .01. The data for extrafoveal and foveal presentations were then analyzed separately and more closely using a within-participants analysis of variance (ANOVA) with variables of hemisphere (LH, RH) and local eccentricity (inner, middle, outer). For extrafoveal words, the ANOVA revealed a strong main effect of hemisphere, by participants, F1(1,15) ⫽ 33.42, p ⬍ .0001, ␩2 ⫽ .72, and by stimuli, F2 (1,63) ⫽ 15.60, p ⬍ .001, ␩2 ⫽ .20, indicating that responses were more accurate when words were projected to the LH than to the RH (72% vs. 65%). No other effects were significant (all Fs ⬍ 1). 2

The primary benefit of the Reicher-Wheeler task for studies of hemispheric asymmetry is that it provides evidence of LH dominance for word recognition that is not contaminated by perceptual bias or guesswork and yet which has repeatedly shown (since its inception by Reicher, 1969) sensitivity to processes of word perception. In particular, one problem often ignored in laterality research is that participants may be more able to guess a word’s identity when words are presented to the right of fixation simply because the highly informative beginnings of words can be seen more easily than when the same words are presented to the left of fixation, and this can produce spurious indications of a LH advantage. The ReicherWheeler task overcomes this problem by using a forced choice between two alternatives that differ in ways that cannot be identified from any other part of the stimulus. Thus, although this crucial aspect of the ReicherWheeler task has not always been fully understood by researchers (e.g., see Lavidor & Bailey, 2005), it is ideal for measuring word recognition performance at different retinal eccentricities without contamination from asymmetries in the visibility of partial word information. The task also avoids biases that occur when overt responses can be produced by only one hemisphere. For example, because speech production in right-handed individuals is lateralized to the LH, using naming as a measure of perceptual performance is likely to produce a spurious advantage for stimuli projected to the LH that does not reflect hemispheric asymmetries in perception.

742

JORDAN, PATERSON, AND STACHURSKI 100

% Accuracy

90

80

LH

RH

70

60

2.20

2.10

2.00

0.35

0.25

.

0.15

0.15

0.25

0.35

2.10

2.00

2.20

50

Retinal Location

Figure 1. Mean percentage of correct responses (%Accuracy) to words presented at each retinal location. LH ⫽ presentations projected to the left hemisphere, RH ⫽ presentations projected to the right hemisphere. Note that overall levels of performance for foveal and extrafoveal displays were deliberately matched. Bars correspond to 95% confidence intervals (e.g., Loftus & Masson, 1994).

For foveal words, the ANOVA showed only a main effect of local eccentricity, F1(2,30) ⫽ 12.07, p ⬍ .0001, ␩2 ⫽ .45, F2(2,126) ⫽ 4.64, p ⫽ .01, ␩2 ⫽ .07. Tukey’s tests showed that responses were more accurate for words at inner eccentricities (69%) than for middle (67%) or outer (63%) eccentricities ( ps ⬍ .01). Crucially, no effect of hemisphere (LH ⫽ 67%, RH ⫽ 67%; all Fs ⬍ 1) and no interaction between hemisphere and local eccentricity (all Fs ⬍ 1.20) were observed for foveal displays.

Discussion The experiment reported in this article was conducted to reevaluate the claim fundamental to SFT (e.g., Ellis, 2004; Lavidor & Ellis, 2003; Lavidor & Walsh, 2004; Shillcock et al., 2000; Shillcock & McDonald, 2005) that each human fovea is split precisely at its vertical midline and, as a consequence, word information at all locations to the left or right of fixation projects unilaterally to the contralateral hemisphere. Thus, although it is well-established that recognition of words in extrafoveal locations is influenced by hemispheric asymmetry because of unilateral contralateral projections, SFT asserts that words presented in foveal locations to the left of fixation also project unilaterally to the RH and words presented in foveal locations to the right of fixation project unilaterally to the LH, and this division in hemispheric processing at the point of fixation produces substantial effects on word recognition. The experiment revealed that, although there was a clear LH advantage for words presented at eccentricities of 2 degrees and more, the same words presented close to fixation (and

falling entirely within foveal vision) produced levels of performance that were the same each side of fixation. Therefore, whereas these findings indicate that functional unilateral projections to different, contralateral hemispheres exist for extrafoveal presentations, the findings provide no evidence of this division in hemispheric processing for foveal presentations (in our experiment, in locations up to 0.90 degrees either side of fixation). Advocates of SFT argue that interhemispheric transmission is costly and hence the proposed anatomical split in each fovea means that projection to the nondominant hemisphere incurs processing costs even in foveal vision (e.g., Brysbaert, 1994; Brysbaert et al., 1996; Hunter et al., 2007; Lavidor et al., 2001). The findings we report do not support this view. Indeed (and notwithstanding the absence of clear anatomical support for foveal splitting), even if an anatomical split in foveal processing actually exists along the lines proposed by advocates of SFT, the findings we obtained suggest that this split has no functional influence on word recognition. Thus, even if human foveae are split anatomically, the transmission of information between the two hemispheres may be sufficiently rapid to obviate a functional role for this anatomical divide. Indeed, as Dehaene, Cohen, Sigman, and Vinckier (2005) point out, callosal projections beyond V1 may have the structure necessary to ensure the continuity of receptive fields across the foveal midline and allow convergence on common visual representations, which may therefore remove the functional impact of any initial foveal split. From the findings of the present study, however, the functional asymmetries in hemispheric processing that were apparent for extrafoveal displays indicate that similar interhemispheric communication is not available for processing words in extrafoveal locations. Clearly, however, the finding that effects of hemispheric asymmetry were absent for foveal presentations is also consistent with the well-established view that a sizable area of overlap exists around the point of fixation within which information projects bilaterally to both hemispheres. However, advocates of SFT have suggested that, even if foveal information does project bilaterally, this information is likely to be highly impoverished, slow to encode, and contribute little to word recognition. For example, Brysbaert (2004) argues on the basis of data from Fendrich et al. (1996) that any bilateral overlap in processing foveal information would not allow fast recognition of small letters and would be too crude for word recognition (see also e.g., Lavidor et al., 2001; Lavidor, Ellison, & Walsh, 2003; Shillcock et al., 2000; Shillcock & McDonald, 2005). Yet, in the present experiment, despite the brevity of each display, the diminutive size of the letters in foveal word stimuli, and the demanding nature of the task (identifying a word from two very similar alternatives), the absence of hemispheric asymmetry for foveal presentations was observed even though performance was considerably above chance for all foveal eccentricities. Indeed, although performance with foveal stimuli showed a classic decline in acuity with increased foveal eccentricity (e.g., Green, 1970; Jones & Higgins, 1947; Polyak, 1941; Riggs, 1965; Weymouth, Hines, Acres, Raaf, & Wheeler, 1928), the close similarity between LH and RH performance remained essentially unchanged at each eccentricity, suggesting that functional bilateral projections for foveal presentations were not restricted to a particular level of visual acuity (or, indeed, to a narrow strip around fixation). Thus, the absence of hemispheric asymmetry in the recognition of foveal stimuli we observed offers no

RE-EVALUATING SPLIT-FOVEA PROCESSING IN WORD RECOGNITION

support for the notion of ineffectual bilateral projections of visual information. Instead, such bilateral projections appear to be sufficient to support identification of brief, small word targets presented at eccentricities extending to at least 0.90 degrees either side of fixation. In fact, on closer inspection of Fendrich et al.’s study, their findings are also consistent with an area of bilateral projection of up to 1 degree either side of fixation (although in their study this was observed after exposure durations of 2 seconds). Moreover, performance in that study was most accurate for spatial frequencies of two and four cycles per degree and least accurate for one and eight cycles per degree, which resembles normal spatial frequency sensitivity. As Fendrich et al. conclude, the precise nature and functioning of the hemispheric overlap remains to be determined but their findings indicate a substantial region of bilateral projection around the point of fixation (of about two degrees wide; a similar conclusion is drawn by Gazzaniga, 2000). This conclusion is inconsistent with the claims of SFT but is consistent with the findings of the present study which implicate a region of bilateral projection that extends at least 0.90 degrees either side of fixation and which supports accurate word recognition. It is clear that the findings we observed offer no support for the conclusions reached in previous research supporting SFT, including research reported by Lavidor et al. (2001); Martin et al. (2007), and by Brysbaert and colleagues (Brysbaert, 1994; Brysbaert et al., 1996; Hunter et al., 2007; see also, Brysbaert, 2004), that word information in foveal vision is processed differently on either side of fixation. However, as argued in the introduction, methodological shortcomings may have contaminated those previous findings. The first concern is that the vast majority of studies reporting support for SFT (including Brysbaert, 1994; Brysbaert et al., 1996; Hunter et al., 2007; Lavidor et al., 2001; Martin et al., 2007; see also Brysbaert, 2004; Ellis, 2004) did not monitor fixation location despite considerable evidence that accurate fixation is difficult to achieve in experimental tasks (Anliker, 1977; Batt et al., 1995; Findlay & Kapoula, 1992; Jones & Santi, 1978; Jordan et al., 1998, 2000, 2003, 2007; Patching & Jordan, 1998; Sugishita et al., 1994; Terrace, 1959). Indeed, previous research into fixation accuracy suggests that when fixation is not controlled using an eye-tracking device, participants often bias their fixations to the right of the required fixation location, and this may explain the effects observed in studies that suggest that information to the right of fixation is more influential than information to the left (e.g., Brysbaert, 1994, 2004; Brysbaert et al., 1996; Hunter et al., 2007; Lavidor et al., 2001; Martin et al., 2007). For example, Jordan et al. (1998; see also Findlay & Kapoula, 1992; Jones & Santi, 1978; Terrace, 1959) used an eye tracker to monitor (but not control) the accuracy of fixating a central fixation point during lateralized word displays. Despite emphasized instructions to fixate accurately, central fixations occurred on only 23% of trials and the majority (64%) of noncentral fixations fell to the right of the required fixation location. Thus, under conditions where accurate fixation is requested rather than ensured, a right-sided bias in fixation location may inspire a visual advantage for information presented to the right of fixation that may then be interpreted (erroneously) as evidence of split-fovea processing. However, other findings suggest that fixation biases can sometimes occur to the left of the required fixation location (e.g., Jordan & Patching, 2006), indicat-

743

ing that, without adequate monitoring and control, the actual locations of fixations made by participants in experiments may be variable and remain undetected. Indeed, variations in fixation accuracy across experiments may explain why findings supporting split-fovea processing are difficult to replicate. Jordan et al. (2008) repeated precisely the experiment reported by Lavidor et al. (2001; see also Skarratt & Lavidor, 2006) in which words were presented at locations straddling a central fixation point so that a variable number of letters were presented to either the left (yea|rn, lovelo|rn) or right (ex|cel, ex|orcise) of this point. Whereas Lavidor et al. reported that increasing the number of letters impaired performance only when this increase occurred to the left of the fixation point (i.e., yea|rn, lovelo|rn), Jordan et al. found no evidence to support this asymmetry. Moreover, in a following experiment in which the actual fixation locations of participants were monitored, it was apparent that participants failed to fixate the designated fixation point on approximately half of the trials, and inaccurate fixations fell at least 0.25 degrees (two letters) away. Thus, not knowing where participants are really fixating in experiments creates substantial problems for the replication of findings and for an accurate understanding of the processes that actually underlie the role of fixation location in word recognition. The second concern is that previous studies (e.g., Brysbaert, 1994; Brysbaert et al., 1996; Hunter et al., 2007; Lavidor et al., 2001; see also Brysbaert, 2004; Ellis, 2004) used stimuli that extended beyond foveal vision and so the benefits observed for stimuli presented to the right of fixation in these studies may have reflected the influence of unilateral extrafoveal projections to LH processes rather than unilateral foveal projections inspired by split-fovea processing. Thus, even if accurate fixation of the designated location were taking place on a trial, information presented to the right of this location would receive beneficial processing because of LH projections from extrafoveal locations, and so provide spurious support for SFT. The problem of extrafoveal overlap was avoided in the foveal displays used in our experiment and no evidence of a role for split-foveal processing in word recognition was obtained. Finally, it is clear that the words and the task used in this study were capable of producing a strong LH advantage for extrafoveal locations and this replicates the findings of previous studies using the Reicher-Wheeler paradigm in lateralized (extrafoveal) displays (e.g., Jordan et al., 1998, 2000, 2003; Reuter-Lorenz & Baynes, 1992). Moreover, because the same words, the same task, the same participants, and the same randomly interleaved design were used for all locations, it seems unlikely that the finding of a LH advantage for extrafoveal words but not foveal words was because of such things as individual differences in hemispheric asymmetry or the use of selective strategies for processing displays in particular locations. Indeed, even the absence of any effect of session indicates that repeating stimuli to achieve the balanced design used in this study did not inspire the results obtained. In addition, the close matching in overall performance between foveal and extrafoveal displays indicates that the absence of a LH advantage for foveal words was not because of different levels of visibility for these stimuli or to the absence of processing these stimuli as words. Indeed, a recently completed study using the same paradigm provides further indications that the effects we observed were because of processes of word perception, in foveal and

744

JORDAN, PATERSON, AND STACHURSKI

extrafoveal displays. In this more recent study (Jordan, Paterson, & Kurtev, 2008), words and matched nonwords were presented in foveal and extrafoveal locations using the same paradigm and the same sized fonts as the present study. The findings showed superior performance for words over nonwords (the classic “wordnonword effect”; e.g., Reicher, 1969) in all retinal locations, indicating that words presented in foveal and extrafoveal locations in this paradigm activate processes of word perception. Moreover, although neither words nor nonwords showed any hemispheric advantage (LH or RH) for foveal locations, only words (but not nonwords) showed a LH advantage for extrafoveal locations, indicating that the LH advantage observed for extrafoveal words in this paradigm reflects processes of word perception. In summary, the findings reported in this article indicate that although a LH advantage occurs when words are presented in extrafoveal locations, no hemispheric advantage (LH or RH) occurs when words are presented in foveal locations. This finding is highly problematic for SFT that proposes a split in each fovea with the result that words in all locations up to the point of fixation project unilaterally to different hemispheres and that this division in processing has substantive effects on word recognition. In contrast, our results provide no support for a functional split in foveal word recognition but are consistent with a substantial area of bilateral projection around the point of fixation within which words are processed equally well on each side of fixation and which supports the accurate recognition of even physically small, briefly presented stimuli.

References Anliker, J. (1977). Eye movements on-line measurement, analysis, and control. In R. A. Monty & J. W. Senders (Eds.), Eye movements and psychological processes. Hillsdale, NJ: Erlbaum. Annett, M. (1970). A classification of hand preference by association analysis. British Journal of Psychology, 61, 303–321. Baayen, R. H., Piepenbrock, R., & Gulikers, L. (1995). The CELEX Lexical Database (Release 2) [CD-ROM]. Philadelphia: Linguistic Data Consortium, University of Pennsylvania. Batt. V., Underwood, G., & Bryden, M. P. (1995). Inspecting asymmetric presentations of words differing in informational and morphemic structure. Brain and Language, 49, 202–223. Blythe, H. I., Liversedge, S. P., Joseph, H. S. S. L., White, S. J., Findlay, J. M., & Rayner, K. (2006). The binocular coordination of eye movements during reading in children and adults. Vision Research, 46, 3898 –3908. Bradshaw, J. L., & Nettleton, N. C. (1983). Human cerebral asymmetry. Englewood Cliffs, NJ: Prentice Hall. Brandt, T., Stephan, T., Bense, S., Yousry, T. A., & Dieterich, M. (2000). Hemifield visual motion stimulation: An example of interhemispheric crosstalk. Neuroreport, 11, 2803–2809. Brysbaert, M. (1994). Interhemispheric-transfer and the processing of foveally presented stimuli. Behavioural Brain Research, 64, 151–161. Brysbaert, M. (2004). The importance of interhemispheric transfer for foveal vision: A factor that has been overlooked in theories of visual word recognition and object perception. Brain and Language, 88, 259 –267. Brysbaert, M., Vitu, F., & Schroyens, W. (1996). The right visual field advantage and the optimal viewing position effect: On the relation between foveal and parafoveal word recognition. Neuropsychology, 10, 385–395. Bub, D. N., & Lewine, J. (1988). Different modes of word recognition in the left and right visual fields. Brain and Language, 33, 161–188. Bunt, A. H., & Minckler, D. S. (1977). Foveal sparing: New anatomical evidence for bilateral representation of the central retina. Archives of Ophthalmology, 95, 1445–1447.

Burgund, E. D., & Marsolek, C. J. (1997). Letter-case-specific priming in the right cerebral hemisphere with a form-specific perceptual identification task. Brain and Cognition, 35, 239 –258. Chiarello, C. (1988). Lateralization of lexical processes in the normal human brain: A review of visual half-field research. In H. A. Whitaker (Ed.), Contemporary reviews in neuropsychology (pp. 36 –76). New York: Springer-Verlag. Crovitz, H. F., & Zener, K. (1962). A group-test for assessing hand- and eye-dominance. American Journal of Psychology, 75, 271–276. Dehaene, S., Cohen, L., Sigman, M., & Vinckier, F. (2005). The neural code for written words: A proposal. Trends in Cognitive Neurosciences, 9, 335–341. Drasdo, N. (1977). The neural representation of visual space. Nature, 266, 554 –556. Ellis, A. W. (2004). Length, formats, neighbours, hemispheres, and the processing of words presented laterally or at fixation. Brain and Language, 88, 355–366. Ellis, A. W., Young, A., & Anderson, C. (1988). Modes of word recognition in the left and right cerebral hemispheres. Brain and Language, 35, 254 –273. Fendrich, R., Wessinger, C. M., & Gazzaniga, M. S. (1996). Nasotemporal overlap at the retinal veridical meridian: Investigations with a callosotomy patient. Neuropsychologia, 34, 637– 646. Findlay, J. M., & Kapoula, Z. (1992). Scrutinization, spatial attention, and the spatial programming of saccadic eye movements. Quarterly Journal of Experimental Psychology, 45A, 633– 647. Fioravanti, F., Inchingolo, P., Pensiero, S., & Spanios, M. (1995). Saccadic eye movement conjugation in children. Vision Research, 35, 3217–3228. Gazzaniga, M. S. (2000). Cerebral specialization and interhemispheric communication: Does the corpus callosum enable the human condition? Brain, 123, 1293–1326. Green, D. G. (1970). Regional variations in the visual acuity for interference fringes on the retina. Journal of Physiology, 207, 351–356. Gronwall, D. M., & Sampson, H. (1971). Ocular dominance: A test of two hypotheses. British Journal of Psychology, 62, 175–185. Hellige, J. B. (1993). Hemispheric asymmetry: What’s right and what’s left? Cambridge, MA: Harvard Press. Hunter, Z., Brysbaert, M., & Knecht, S. (2007). Foveal word reading requires interhemispheric communication. Journal of Cognitive Neuroscience, 19, 1373–1387. Jones, B., & Santi, A. (1978). Lateral asymmetries in visual perception with and without eye movements. Cortex, 14, 164 –168. Jones, L. A., & Higgins, G. C. (1947). Photographic granularity and graininess III: Some characteristics of the visual system of importance in the evaluation of graininess and granularity. Journal of the Optical Society of America, 37, 217–263. Jordan, T. R., & Patching, G. R. (2003a). Perceptual interactions between bilaterally presented words: What you get is often not what you see. Neuropsychology, 17, 566 –577. Jordan, T. R., & Patching, G. R. (2003b). Assessing effects of stimulus orientation on perception of lateralized words and nonwords. Neuropsychologia, 41, 1693–1702. Jordan, T. R., & Patching, G. R. (2006). Assessing effects of fixation demands on perception of lateralized words: A visual window technique for studying hemispheric asymmetry. Neuropsychologia, 44, 686 – 692. Jordan, T. R., Patching, G. R., & Milner, A. D. (1998). Central fixations are inadequately controlled by instructions alone: Implications for studying cerebral asymmetry. Quarterly Journal of Experimental Psychology, 51A, 371–391. Jordan, T. R., Patching, G. R., & Milner, A. D. (2000). Lateralized word recognition: Assessing the role of hemispheric specialization, modes of lexical access and perceptual asymmetry. Journal of Experimental Psychology: Human Perception and Performance, 26, 1192–1208.

RE-EVALUATING SPLIT-FOVEA PROCESSING IN WORD RECOGNITION Jordan, T. R., Patching, G. R., & Thomas, S. M. (2003a). Assessing the role of hemispheric specialization, serial-position processing and retinal eccentricity in lateralized word perception. Cognitive Neuropsychology, 20, 49 –71. Jordan, T. R., Patching, G. R., & Thomas, S. M. (2003b). Asymmetries and eccentricities in studies of lateralized word recognition: A response to Nazir. Cognitive Neuropsychology, 20, 81– 89. Jordan, T. R., & Paterson, K. B. (2008). Re-evaluating split-fovea processing in word recognition: A critical assessment of recent research. Neuropsychologia, in press. Jordan, T. R., Paterson, K. B., & Kurtev, S. (2008). The word-nonword effect in foveal and extrafoveal displays. Manuscript in preparation. Jordan, T. R., Paterson, K. B., & Stachurski, M. (2008). Re-evaluating split-fovea processing in word recognition: Effects of word length. Cortex, in press. Jordan, T. R., Paterson, K. B., Stachurski, M., Kurtev, S., & Xu, M. (2007). Evaluating the influence of fixation location on perception of centrallypresented words: Some researchers (and all participants) may be missing the point. Paper presented at Joint meeting of the Experimental Psychology Society and Psychonomic Society, 4 –7 July, Edinburgh. Jordan, T. R., Redwood, M., & Patching, G. R. (2003). Effects of form familiarity on perception of words, pseudowords, and nonwords in the two cerebral hemispheres. Journal of Cognitive Neuroscience, 15, 537–548. Juhasz, B. J., Liversedge, S. P., White, S. J., & Rayner, K. (2006). Binocular co-ordination of eye movements during reading: Word frequency and case alternation affect fixation duration but not binocular disparity. Quarterly Journal of Experimental Psychology, 59, 1614 –1625. Kirkby, J. A., Webster, L. A. D., Blythe, H. I., & Liversedge, S. P. (2008). Binocular coordination during reading and non-reading tasks. Psychological Bulletin, in press. Lavidor, M., Babkoff, H., & Faust, M. (2001). Analysis of standard and non-standard visual format in the two hemispheres. Neuropsychologia, 39, 430 – 439. Lavidor, M., & Bailey, P. J. (2005). Dissociations between serial position and number of letters effects in lateralized visual word recognition. Journal of Research in Reading, 28, 258 –273. Lavidor, M., Ellis, A. W., Shillcock, R., & Bland, T. (2001). Evaluating a split processing model of visual word recognition: Effects of word length. Cognitive Brain Research, 12, 265–272. Lavidor, M., Ellison, A., & Walsh, V. (2003). The cortical representation of centrally presented words: A magnetic stimulation study. Visual Cognition, 10, 341–362. Lavidor, M., & Walsh, V. (2004). The nature of foveal representation. Nature Reviews Neuroscience, 5, 729 –735. Leff, A. P. (2004). A historical review of the representation of the visual field in primary visual cortex with special reference to the neural mechanisms underlying macular sparing. Brain and Language, 88, 268 –278. Leventhal, A. G., Ault, S. J., & Vitek, D. J. (1988). The nasotemporal division in primate retina: The neural bases of macular sparing and splitting. Science, 240, 66 – 67. Lindell, A. K., & Nicholls, M. E. R. (2003). Cortical representation of the fovea: Implications for visual half-field research. Cortex, 39, 111–117. Liversedge, S. P., Rayner, K., White, S. J., Findlay, J. M., & McSorley, W. (2006). Binocular co-ordination of the eyes during reading. Current Biology, 16, 1726 –1729. Liversedge, S. P., White, S. J., & Rayner, K. (2006). Binocular coordination of eye movements during reading. Vision Research, 46, 2363–2374. Loftus, G. R., & Masson, M. E. J. (1994). Using confidence intervals in within-subjects designs. Psychonomic Bulletin & Review, 1, 476 – 490. Martin, C. D., Nazir, T., Thierry, G., Paulignan, Y., & Demonet, J. F. (2006). Perceptual and lexical effects in letter identification: An eventrelated potential study of the word superiority effect. Brain Research, 1098, 153–160.

745

Martin, C. D., Thierry, G., De´monet, J. F., Roberts, M., & Nazir, T. (2007). ERP evidence for the split fovea theory. Brain Research, 1185, 212–220. Miles, W. R. (1930). Ocular dominance in human adults. Journal of General Psychology, 3, 412– 430. Mishkin, M., & Forgays, D. G. (1952). Word recognition as a function of retinal locus. Journal of Experimental Psychology, 43, 43– 48. O’Regan, J. K. (1981). The convenient viewing position hypothesis. In D. F. Fisher, R. A. Monty, & J. W. Senders (Eds.), Eye movements, cognition, and visual perception (pp. 289 –298). Hillsdale, NJ: Erlbaum. Patching, G. R., & Jordan, T. R. (1998). Increasing the benefits of eyetracking devices in divided visual field studies of cerebral asymmetry. Behavior Research Methods, Instruments, & Computers, 30, 643– 650. Polyak, S. L. (1941). The retina. Chicago: University of Chicago Press. Porac, C., & Coren, S. (1976). The dominant eye. Psychological Bulletin, 83, 880 – 897. Porta, G. (1593). De refractione. Optices parte: Libri novem. Napoli: Ex officina horatii salviani, apud Jo. Jacobum Carlinum, & Anotnium Pacem. Rayner, K., & Pollatsek, A. (1989). The Psychology of Reading. Englewood Cliffs, NJ: Prentice-Hall. Reicher, G. M. (1969). Perceptual recognition as a function of meaningfulness of stimulus material. Journal of Experimental Psychology, 81, 275–280. Reinhard, J., & Trauzettel-Klosinski, S. (2003). Nasotemporal overlap of retinal ganglion cells in humans: A functional study. Investigative Ophthalmology & Visual Science, 4, 1568 –1572. Reuter-Lorenz, P. A., & Baynes, K. (1992). Modes of lexical access in the callosotomized brain. Journal of Cognitive Neuroscience, 4, 155–164. Riggs, L. A. (1965). Visual acuity. In C. H. Graham (Ed.), Vision and visual perception (pp. 321–349). New York: Wiley. Roth, H. L., Lora, A. N., & Heilman, K. M. (2002). Effects of monocular viewing and eye dominance on spatial attention. Brain, 125, 2023–2035. Shillcock, R., Ellison, T. M., & Monaghan, P. (2000). Eye-fixation behavior, lexical storage, and visual word recognition in a split processing model. Psychological Review, 107, 824 – 851. Shillcock, R. C., & McDonald, S. A. (2005). Hemispheric division of labour in reading. Journal of Research in Reading, 28, 244 –257. Skarratt, P. A., & Lavidor, M. (2006). Magnetic stimulation of the left visual cortex impairs expert word recognition. Journal of Cognitive Neuroscience, 18, 1749 –1758. Stone, J. (1966). The naso-temporal division of the cat’s retina. Journal of Comparative Neurology, 126, 585– 600. Stone, J., Leicester, J., & Sherman, S. M. (1973). The naso-temporal division of the monkey’s retina. Journal of Comparative Neurology, 150, 333–348. Sugishita, M., Hamilton, C. R., Sakuma, I., & Hemmi, I. (1994). Hemispheric representations of the central retina of commissurotomized subjects. Neuropsychologia, 32, 399 – 415. Terrace, H. S. (1959). The effects of retinal locus and attention on the perception of words. Journal of Experimental Psychology, 58, 382–385. Trauzettel-Klosinski, S., & Reinhard, J. (1998). The vertical field border in hemianopia and its significance for fixation and reading. Investigative Ophthalmology & Visual Science, 39, 2177–2186. Weymouth, F. W., Hines, D. C., Acres, L. H., Raaf, J. E., & Wheeler, M. C. (1928). Visual acuity within the area centralis and its relation to eye movements and fixation. American Journal of Ophthalmology, 11, 947–960. Young, A. W., & Ellis, A. W. (1985). Different methods of lexical access for words presented in the left and right visual hemifields. Brain and Language, 24, 326 –358.

Received February 22, 2008 Revision received June 4, 2008 Accepted June 6, 2008 䡲