Attentional Resource Demands of Visual Word Recognition in Naming ...

Journal of Experimental Psychology: Human Perception and Performance 1992, Vol. 18. No. 2. 460-470

Copyright 1992 by the American Psychological Association, Inc. 0096-l523/92/$3.00

Attentional Resource Demands of Visual Word Recognition in Naming and Lexical Decisions

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Chris M. Herdman Carleton University, Ottawa, Ontario, Canada Attentional demands of lexical access were assessed with dual-task methodology. Subjects performed an auditory probe task alone (single-task) or combined (dual-task) with either a lexical decision or a naming task. In Experiment 1, probe performance showed a decrement from singleto dual-task conditions during recognition of words in both lexical decision and naming tasks. In addition, decrements in probe performance were larger during processing of low-frequency compared with high-frequency words in both of the word recognition tasks. Experiment 2 showed that the time course of frequency-sensitive demands was similar across lexical decision and naming tasks and that attention is required early in the word recognition sequence. The results support the assumption that lexical access is both frequency sensitive and attention demanding.

Much of the research in the reading literature has been focused on identifying the specific processes activated during reading and determining how these processes interact. An assumption often made in this research is that processing interactions occur as a result of competition for a limited supply of attentional resources (e.g., Baddeley, 1986; Daneman & Carpenter, 1980, 1983; LaBerge & Samuels, 1974; Perfetti, 1985; Stanovich, 1980, 1981). A resource-interaction approach to reading is plausible in that reading clearly requires attention: Even skilled readers have difficulty time-sharing between reading and a second, relatively simple task such as monitoring for an auditory probe (Inhoff & Fleming, 1989; see also Hirst, Spelke, Reaves, Caharack, & Neisser, 1980). However, it is not clear which of the many processes that are active during reading require resources. For beginning readers, lexical access may be the primary source of attentional demands.' Theorists have proposed that the attentional demands of lexical access limit reading performance by restricting the amount of resources available for other reading processes (Perfetti, 1985; Perfetti & Lesgold, 1979; Samuels & Kamil, 1984). As readers become more experienced, however, lexical access may become automatic (LaBerge & Samuels, 1974). Automatic processes are fast, activated without intention, and do not require resources (Hasher & Zacks, 1979; Posner & Snyder, 1975; Schneider & Shiffrin, 1977;Shiffrin&Dumais, 198 l;Shifrrin& Schneider, 1977). Accordingly, lexical access in adult readers would

presumably not compete with other reading processes for attentional resources. Research on contextual priming and interference (i.e., Stroop tasks) supports the notion that as reading skill develops, lexical access becomes automatic insofar as it occurs rapidly (Baddeley, Logic, Nimmo-Smith, & Brereton, 1985; Frederiksen, 1978,1981; Perfetti, 1985) and without intention (Humphreys, 1985; Kahneman & Chajczyk, 1983; Logan, 1980). In contrast, research using dual-task methods has shown that resources are required to recognize words in lexical decision tasks and thus that lexical access may not be strictly automatic (Becker, 1976; Herdman & Dobbs, 1989; Kellas, Ferraro, & Simpson, 1988; Mullin & Egeth, 1989). However, because controversy exists over the use of lexical decision tasks to examine word recognition (Balota & Chumbley, 1984; see also Besner & McCann, 1987; Paap, McDonald, Schvaneveldt, & Noel, 1987), it is important to assess attentional demands in other tasks that involve lexical access (Humphreys, 1985). The present research (a) examines whether lexical access requires resources in the context of a naming task and (b) provides evidence concerning the locus of word frequency effects in naming and lexical decisions. Theoretical Approach and Background Research Theorists in the word recognition literature typically have not made assumptions about resource demands (e.g., Forster, 1976; Gordon, 1983; Paap, Newsome, McDonald, & Schvaneveldt, 1982). One exception is Becker (1976, 1979, 1980, 1985; Becker & Killion, 1977; Eisenberg & Becker, 1982), who explicitly outlined the attentional demands of lexical access in his verification model. Becker divided lexical access into two processes: feature extraction and verification. Feature extraction is an automatic process that creates a set of candidate words that are consistent with the sensory attributes of the stimulus. Verification involves selecting an item from the

This research was supported by an operating grant from the Natural Sciences and Engineering Research Council of Canada to Chris M. Herdman. Donna Chernecki, Mark Cornblat, and Kim Stolpmann assisted with data collection. Valuable comments on an earlier version of this article were provided by Glyn Humphreys, Sandy Pollatsek, and an anonymous reviewer. Special thanks are extended to Jo-Anne LeFevre for her insightful contributions throughout the research. Correspondence concerning this article should be addressed to Chris M. Herdman, Department of Psychology, Carleton University, Ottawa, Ontario, Canada K.1S 5B6. Electronic mail may be sent to CHRIS [email protected].

1 In accord with Paap, McDonald, Schvaneveldt, and Noel (1987), lexical access is equated with word recognition and is defined as the process in which a unitary interpretation of a stimulus is made available.

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candidate set, combining the relational information stored with that item with the primitive features that were previously extracted, and comparing the constructed representation to the item's representation in sensory memory. An item is recognized as a word when the match between the constructed and the sensory representations is successful. The candidate set is ordered according to frequency such that high-frequency items are submitted for verification first. According to Becker (1976), the attentional demands of lexical access are isolated in the verification stage. Because verification is assumed to be sensitive to word frequency, more attention should be required to recognize low-frequency than high-frequency words. To test this assumption, Becker (1976) used a dual-task paradigm in which subjects were required to perform a lexical decision and an auditory probe task concurrently. The complexity of the auditory task was varied from simple detection to a choice condition. Attentional demands associated with recognition of words in the lexical decision task were reflected in responses to auditory probe stimuli. The results showed a small effect of complexity during concurrent recognition of high-frequency words but a large effect during recognition of low-frequency words, supporting the notion that more attentional resources are required to recognize low- compared with high-frequency words. Becker's (1976) findings have been corroborated by Herdman and Dobbs (1989), who used a dual-task change paradigm to assess the attentional demands of lexical access. In the standard dual-task paradigm (such as the one used by Becker, 1976), subjects are presented with primary and secondary task stimuli and are required to respond to both. In the change paradigm, secondary task stimuli are presented on only a proportion of the dual-task trials. When a secondary task stimulus is presented, subjects forfeit a response to the primary task stimulus and respond only to the secondary task stimulus. Attentional demands associated with processing the primary task stimulus are reflected in single- to dual-task decrements in secondary task performance. One advantage of the change paradigm over the standard dual-task paradigm is that response competition is minimized because subjects do not respond to primary task stimuli when a secondary response is required (Logan & Burkell, 1986). A second advantage of the change paradigm is that responses to secondary task stimuli are not dependent on the time taken to respond to primary task stimuli. This is of particular concern when primary task responses vary with the nature of the primary task stimuli (cf. Becker, 1976). Herdman and Dobbs (1989) required subjects to perform lexical decisions while concurrently monitoring for the presentation of auditory probe tones. Performance on the probe task was found to decrement from single- to dual-task conditions. Moreover, decrements in probe task performance were greater during recognition of low-frequency as compared with high-frequency words. These results are consistent with Becker's (1976) notion that frequency-sensitive processes in lexical access (i.e., verification) require attentional resources. A critical assumption underlying Becker's (1976) and Herdman and Dobbs's (1989) research is that frequency effects in lexical decisions reflect characteristics of lexical access. It has

been suggested, however, that postlexical processes in the lexical decision task are also frequency sensitive (Balota & Chumbley, 1984: however, see Paap et al., 1987). In this view, frequency-sensitive demands assessed in lexical decisions may reflect not only the demands associated with lexical access (e.g., verification) but also the demands associated with processes that occur postlexically. A more extreme possibility is that lexical access is automatic (LaBerge & Samuels, 1974) and that the resource demands incurred in the lexical decision task are entirely postlexical. In either case, and as noted previously by Humphreys (1985), it is clearly necessary to examine the attentional demands of lexical access using a task other than lexical decisions. Naming tasks, in which subjects are required to pronounce words as quickly as possible, have also been used extensively to examine word recognition. Postrecognition processes in naming have been characterized as being minimally sensitive to word frequency because, unlike the lexical decision task, binary decisions are not required to make a naming response (Balota & Chumbley, 1984; Monsell, Doyle, & Haggard, 1989).

Present Research Two experiments are reported in which the resource demands of recognition were compared in naming and lexical decision tasks. In both experiments, attentional demands were assessed using a dual-task change paradigm similar to that used by Herdman and Dobbs (1989; see also Kellas et al., 1988; Paap & Noel, 1989). Becker's (1976, 1979, 1980, 1985; Becker & Killion, 1977; Eisenberg & Becker, 1982) verification model was used as a theoretical framework for this research because it includes explicit assumptions concerning the resource demands of lexical access. One modification of Becker's model was necessary to accommodate the role of phonological codes important for naming. In accord with Paap et al. (1987; see also Carr & Pollatsek's, 1985, interpretation of the verification model), it was assumed that phonological activation occurs postlexically, such that knowledge about a word's pronunciation is made available after verification is completed. In this view, assumptions concerning the attentional demands of lexical access should be the same for naming as for lexical decision tasks: In both tasks resources should be required during verification, and more resources should be required to verify low- as compared with highfrequency words.

Experiment 1 Subjects performed either a naming or a lexical decision task alone (single task) and then combined with an auditory probe task (dual task). The primary measure of attentional demands was performance on the auditory probe task. Herdman and Dobbs (1989) found evidence for frequency-sensitive demands in lexical decisions when probes were presented 167 ms after letter strings. Therefore, a stimulus onset asynchrony (SOA) of 167 ms was used in Experiment 1. In accord with Becker (1976), the demands of verification should limit the availability of resources for processing probe tones in the dual task. On the assumption that verification occurs in both naming and lexical decisions, recognition of words in both


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tasks should result in performance decrements on the probe task. Performance decrements will be reflected in longer probe latencies in the dual- than the single-task condition. On the assumption that the demands of lexical access vary with word frequency (Becker, 1976; Herdman & Dobbs, 1989), decrements in probe task performance should be larger during recognition of low-frequency than high-frequency words. Alternative predictions would be necessary if it were assumed that frequency-sensitive demands occur postlexically, that is, after verification. In this view, frequency-sensitive decrements in probe performance during lexical decisions would still be predicted: These decrements could be attributed to postlexical decision processes in the lexical decision task. However, on the assumption that postlexical processes in naming are not sensitive to frequency (Balota & Chumbley, 1984; Monsell et al., 1989), decrements in probe performance during naming should not vary with word frequency. It should be noted that performance decrements may occur because of concurrence costs associated with time-sharing tasks (Navon & Gopher, 1979). Because costs may be greater to time-share the probe task with one or the other recognition task, the absolute size of decrements on the probe task is not informative. Instead, it is necessary to consider differential decrements across factors presumed to require resources. Therefore, of primary importance in the present research are differential decrements on high- versus low-frequency trials. To summarize, Experiment 1 examines the assumption that frequency-sensitive processes underlying lexical access require attention. In accord with Becker (1976), performance on the probe task is expected to decrement from single- to dual-task conditions, and these decrements should vary depending on the frequency of the word being processed. On the assumption that words must be verified in both naming and lexical decision tasks, frequency-sensitive decrements in probe performance should be found for both naming and lexical decisions. On the other hand, if word frequency influences postlexical but not lexical processes, then frequencysensitive decrements in probe performance should be observed only during processing of words in the lexical decision task.

Method

Subjects A total of 37 undergraduate students participated to partially fulfill a course requirement. The data of 5 subjects were not included in the analyses because these subjects were unable to perform the auditory task. This left a total of 32 subjects, 16 in the naming condition and 16 in the lexical decision condition.

Apparatus A MicroTech Unlimited laboratory computer was used to present words on a Panasonic video monitor (Model WV-5300), to generate the probe (333 Hz) and distractor (313 Hz) tones over a pair of Scintrex MKJI headphones, and to record responses and latencies. A Grason-Stadler model E7300A-1 voice-activated relay (VOR) was interfaced with the computer to collect naming and lexical decision latencies.

Subjects were seated approximately 50 cm in front of the video monitor. A response panel was located vertically in front of the subjects. It contained three keys, one located at the center of the panel, one 8 cm above center, and another 8 cm below center. Subjects used the center key to start trials, the upper key to indicate that a probe tone had been detected, and the lower key to signal the end of the trial. Subjects were instructed to make all keypresses by using the index finger of their preferred hand. Procedure Subjects were assigned to either the naming or the lexical decision task. A session consisted of three blocks of trials: practice, single-task baseline, and dual task. The practice block consisted of 32 single-task word recognition trials (i.e., either naming or lexical decisions), followed by 32 single-task auditory trials and then 32 dual-task trials. The single-task baseline condition consisted of 52 word recognition trials followed by 52 probe trials. The first four trials in each condition served as practice. The dual-task condition consisted of 208 (16 practice + 192 experimental) dual-task trials. In the single-task naming condition, subjects fixated on a centrally presented dot and started trials by pushing and holding in the center key. After 500 ms, the fixation dot was replaced by a letter string, and subjects pronounced the word as quickly as possible. The center key was held in throughout the trial. After 2,000 ms had elapsed, a "reset" message appeared, and the subjects pressed the lower key to end the trial. The word disappeared from the screen when the VOR was activated or if the center key was released. The procedure in the single-task lexical decision condition was the same except that subjects were to say "word" when a word had been presented and "nonword" when a nonword was presented. Verbal responses to the lexical decision were used to maintain separation between lexical and probe responses and thereby minimize the possibility of response competition (see Herdman & Dobbs, 1989). In the single-task auditory condition, the fixation dot was replaced by a string of five asterisks. The asterisks were presented to simulate the procedure that would be used in the dual-task condition. When a distractor (low pitch) tone was presented, subjects continued holding in the center key until a "reset" message appeared and they were to press the lower key to end the trial. On "probe" trials, subjects released the center key as quickly as possible upon detection of a probe (high pitch) tone and then pushed the top key. In the dual-task condition the fixation dot was replaced by a letter string. On distractor trials, subjects were instructed to continue with the word recognition component of the dual task. That is, subjects in the naming task were to name the word, and subjects in the lexical decision task were to make a lexical decision response. On probe trials, subjects were instructed to quickly respond to the probe tone by releasing the center key and then pressing the top key. That is, when a probe tone was detected, the word recognition component of the dual task was forfeited and priority was given to making a probe response. This represents the change component of the dual task. Probe tones were presented on 25% of the trials, and distractor tones were presented on the other 75%, the same percentages used by Herdman and Dobbs (1989). Subjects were instructed to respond as quickly and as accurately as possible. In the single-task auditory condition and the dual-task condition, subjects were informed that probe tones would be presented on only 25% of the trials. For the dual task, subjects were encouraged to begin processing the words as soon as they appeared on the screen. Subjects were instructed to protect performance on the word recognition task by allocating attention to this task but to respond to the probe as quickly as possible. Single-task naming and lexical decision latencies were measured from presentation of a letter string until activation of the VOR. In

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the dual-task condition, subjects were required to refrain from making a word recognition response until they had determined that a distractor tone had been presented. To compensate for the delay imposed by the 167-ms SOA, dual-task word recognition latencies were measured from the onset of the distractor tone. Responses to probe tones were measured as the time between the presentation of a probe tone until the release of the start key. Previous research has shown that this measure reflects overlap in demand for attentional resources between the word recognition task and the auditory probe task (Herdman & Dobbs, 1989; see also Herdman & LeFevre, in press; Keele, 1973). The top key on the response panel was used to ensure that subjects had intended to make a probe response and had not accidentally removed their fingers from the center key.

Stimulus Materials Naming task. Words ranging from 4 to 6 letters in length were selected from Kucera and Francis (1967). Sixty-four words were used in the practice session. Half were used for the single-task naming practice trials and half for the dual-task practice trials. A total of 240 words were used in the experiment proper (i.e., 48 single-task and 192 dual-task, excluding practice trials). Of the 192 dual-task words, 48 were items presented during probe trials, 12 of which were high-frequency words and 12 low-frequency words. The high-frequency probe-trial words had a mean frequency of 304 (SD = 236); low-frequency probe-trial words had a mean frequency of 1.75 (SD = 1.06). The high- and low-frequency probe words were matched for length and as closely as possible for digram frequency using the norms provided by Mayzner and Tresselt (1965). The remaining 24 probe-trial words were fillers. These were a mix of low-, medium-, and high-frequency words, with a mean frequency of 22.7 (SD = 4.28). Another 24 words (12 high- and 12 low-frequency) were designated as "critical" items that were used to compare dualtask naming latencies (i.e., when a distractor tone had been presented) with single-task naming latencies. The high- and low-frequency critical items had mean frequencies of 278.7 (SD = 169.55) and 1.67 (SD = 0.49), respectively. Of the 48 single-task words, 24 (12 highand 12 low-frequency) were also designated as critical items. These were matched to the dual-task critical words for frequency and length. The high- and low-frequency items had mean frequencies of 278.1 (SD = 189.1) and 1.92 (SD = 0.79), respectively. The single- and dual-task critical items were interchanged such that for every subject receiving a critical item in the single task, another subject received it in the dual task. The remaining single- and dual-task words were a mixture of high-, medium-, and low-frequency items with a mean frequency of 77.04 (SD = 109.0). The words used on the single-task condition were randomized with the restriction that half of the high-frequency words and half of the low-frequency words were presented in each half of the set. In the dual-task condition, order was constrained in that (a) 25% of each half of a set were probe trials, (b) 25% of the probe trials in each half of the set occurred when a high-frequency word was presented and 25% when a low-frequency word was presented, and (c) half of the critical items were presented in each half of the set, half of these being high-frequency words. Lexical decision task. Half of the words from the naming task were used in the lexical decision task. Nonwords were formed by changing one letter of a word. In the practice session there were 32 words and 32 nonwords (half of each for single-task trials and half for dual-task trials). A total of 240 letter strings (120 words and 120 nonwords) were used in the experiment proper, 48 (24 words, 24 nonwords) in the single task and 192 (96 words, 96 nonwords) in the dual task. Of the 192 dual-task letter strings, 48 (24 words and 24 nonwords) were presented during probe trials. The words used for

the probe trials were the same high- and low-frequency words used for the probe trials in the naming condition. The single- and dualtask critical words were also the same as in the naming condition.

Results and Discussion The primary measure of probe and word recognition performance was response latency. Mean correct latencies within each condition were computed for each subject. Latencies greater than 2.5 standard deviations from the mean of the respective condition were defined as outliers and removed from the data set, and the means were recomputed. The pattern of results was not changed with the removal of outlier scores. Fewer than 1 % of the naming and lexical decision responses were lost because of apparatus failure. Of central interest were the effects of processing high- versus low-frequency words on responses to auditory probes.

Auditory Probe Responses Mean single- and dual-task auditory probe latencies are shown in Table 1. In order to assess dual-task performances relative to single-task baseline levels, decrement scores were computed by subtracting each subject's single-task score from the corresponding dual-task score. The use of decrement scores is particularly appropriate for examining changes in performance on the probe task because there is only one measure of single-task performance for each dual-task factor. The probe decrement data were analyzed with a 2 (Frequency: high vs. low) x 2 (Task: naming vs. lexical decision) analysis of variance (ANOVA) with repeated measures on the first factor. The assumption that the demands of recognition vary with word frequency was supported by a significant effect of frequency, F(\, 30) = 17.32, M5e = 1,589.0 \,p< .001. In accord with the verification model, decrements in probe performance were greater during recognition of low- than high-frequency words (decrements of 93 ms and 52 ms, respectively). No other main effects nor any interactions were significant. To confirm that recognition of words in both lexical decision and naming tasks resulted in frequency-sensitive demands, separate analyses of the probe decrements were performed for each task. These analyses showed that decrements in probe performance were greater during processing of low-

Table 1 Mean Correct Auditory Probe and Word Recognition Latencies: Experiment 1 Auditory probe Dual Condition Naming

Single 467

HF 498

LF 541

Word recognition Single HF 591

LF 644

Dual HF 738

LF 768

Lexical decision 416 488 529 715 850 829 938 Note. Values are in milliseconds. Stimulus onset asynchrony in both conditions was 167 ms. HF and LF refer to high- and low-frequency trials, respectively.

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as compared with high-frequency words in both lexical decisions,/^!, 15) = 9.46, MS, = 1,400.45,p