Temporal localization of the response selection ... - Science Direct

INTERNATIONAL JOURNAL OF PSYCHOPHYSIOLOGY International

Journal

of Psychophysiology

19 (1995) 257-261

Temporal localization of the response selection processing stage Jean-Louis

Nandrino,

Farid El Massioui

*

Unite’ de Recherche en Psychophysiologie Cognitive, LENA CNRS URA 654, Uniuersite’ Paris 6, H6pital de la Salpt?tri&e, 47 Bd de l’H6pita1, 75651 Paris Ceder 13, France Received

14 April 1994; accepted

28 February

1995

Abstract Response choice is one of the stages in the information processing model proposed by Sanders. It is influenced by stimulus-response (S-R) compatibility. Segmentation of the processing window in intervals between RT and peak latencies and between peak latencies, was used to test the assumption that the decisional processes would be

concomitant with the N200 rather than the P300 component. ERPs were recorded in ten subjects during a spatial S-R compatibility auditory task. The S-R compatibility effect is observed on P300 latencies but is only a trend on the N200 component. An effect also observed on the interval between RT and N200 and especially between N200 and P300 while no effect is observed on the interval between RT and P300. These results support the idea that the selection processes ending with P300 occurrence could start as early as the N200 peak component. Keywords: Mental

chronometry;

Information

processing;

Mental chronometry has concentrated on the fundamental question of the existence of separate components of mental processes that mediate overt responses to stimuli and take measurable amounts of time (Meyer et al., 1988). Based on Sternberg’s additive factors method (Sternberg, 19691, which allows the identification of information processing stages from patterns of additive and interactive relations between experimental variables, Sanders (Sanders, 1980; Sanders, 1990) proposed a general model where each stage was associated with an experimental variable. Each of these variables was assumed to act on the associated stage. One of these stages is

* Corresponding

author. Fax: (+33-l)

0167-8760/95/$09.50 0 1995 Elsevier SSDI 0167-8760(95)00017-8

44 24 39 54. Science

ERPs;

N200; P300; Stimulus-response

compatibility

response choice, considered to be a crucial node between sensory and motor systems. According to Sanders, this stage is influenced by stimulus-response (S-R) compatibility. The effect of this variable is generated by the conflict to select the appropriate correspondence between stimulus set and response set. The difficulty in this case is to reduce interfering effects provided by wrong stimuli and/or wrong responses. With regard to their temporal resolution in millisecond steps, event-related potentials (ERP) allow clarification of timing, ordering, and interactions between the different intermediate processes involved in a specific cognitive task (Hillyard and Kutas, 1983). ERP components, and particularly their latenties, are useful tools to localize information processing stages and to measure their duration. The

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258

J.-L. Nandrino, F.E. Massioui/International

P300 component is often described as sensitive to the S-R compatibility variable (Ragot, 1984; Pfefferbaum et al., 1980, 1986; Fiori et al., 1992). In other studies, it is also affected by an increase in memory set size (Pfefferbaum, 1980; Ford et al., 1982). Moreover, task demands determine subject strategies which could require different types of processing (Pfefferbaum et al., 1986) and consequently affect the P300 onset (Kutas et al., 1977; Donchin and Coles, 1988). These results (for a review Ragot, 1990) challenge the interpretation whereby P3GO is considered as indexing the end of stimulus evaluation processes (Kutas et al., 1977; MacCarthy and Donchin 1981; Magliero et al., 1984). These arguments suggest that the P300 complex would reflect later cognitive processes in addition to sensorial analysis. Perceptual and motor processes could be co-activated within the P300 time window (Renault et al., 1988). This co-activation could be reflected by the two subcomponents of P300 described by Falkenstein et al. (Falkenstein et al., 1993; Falkenstein et al., 1994) the first subcomponent being sensitive to stimulus evaluation and the second related to response selection processes. It seems nevertheless surprising that response selection activity which determines further motor processes occurs so late and could be associated with the P300. When P300 occurs later than RT (Donchin et al., 1978; MacCarthy and Donchin, 1983) decisional processes obviously precede behavioral response. In regard to the stronger relationship between N200 and RT than between P300 and RT (Renault et al., 1982; Ritter et al., 19821, the N200 component is more likely to be linked with some of motor processes and could be the appropriate index of response selection (Ragot and Renault, 1985). To date, this assumption has been suggested only in a preliminary study presented by Bashore (Bashore, 19901. The aim of the present study was to test the more acceptable hypothesis that such decisional processes (response selection) would occur earlier than P300 and would be concomitant with the N200 component. To test this assumption, we used a subtraction procedure which provides additional dependent variables (intervals between ERPs peak latencies). An effect of an experimen-

Journal of Psychophysiology 19 (1995) 257-261

tal variable on any of these time segments implies that this variable is processed during this time window (Renault et al., 1988). Ten volunteers (6 women and 4 men, aged 21-35 years), unpaid and right handed, were asked to respond to tones (150 ms duration), randomly distributed to each ear through headphones. The task was to press a button, as quickly as possible, with the right index finger in response to low tones (550 Hz) and with the left index finger in response to high tones (1500 Hz). S-R compatibility was manipulated here implicitly. This means that subjects were not aware of the different compatibility conditions (Ragot 1990). Averaging of responses received by the ear on the same side (compatible condition) and those received by the opposite ear to the responding hand (non-compatible condition) was done offline. Inter-stimulus interval (ISI) varied randomly between 1300 and 1800 ms. ERPs were recorded with four equally spaced mid-line electrodes (Ag/AgCl) Fpz-Fz-Cz-Pz, referred to the nose. The band pass of the amplifiers was 0.08-40 Hz. Horizontal and vertical electro-oculograms were recorded in order to detect records contaminated with eye movements and blinks. Data were digitized at a 125 Hz sampling rate, averaged and displayed off-line by a PDP 11/73 computer, after excessive ocular potentials and other artifacts were eliminated. Only trials free of behavioral errors were analyzed. The pre-stimulus baseline was 200 ms. The length of the averaging window was 990 ms including 100 ms pre-stimulus. ERP components are measured in the 70-130 ms range for NlOO, in the 150-300 ms range for N200, and in the 250-550 ms range for P300. For each component, the peak latency is the maximum amplitude recorded in the corresponding time window. This amplitude computation is performed from an interpolation of the EEG signals. A dominant frontal topography was obtained for the NlOO and N200 components, and a dominant parietal topography for P300. ERP peak latencies and intervals obtained from subtractions between reaction time CRT) and these peaks, or between the different peaks themselves were used to segment the reaction

J.-L. Nandrino, F.E. Massioui /International

Journal of Psychophysiology

time window. This segmentation provides a supplementary class of indices to better identify information processing stages. When an effect of an experimental variable is observed on a given interval, we assume that this variable is processed during this time window (Renault et al., 1988). In the present view of stimulus-response activity, the intervals change automatically according to ERP latencies and RT variations. Since ERP components and RT depend on several parameters such as task demands, their relationship is not necessarily stable. S-R non-compatibility increases RTs Ml,91 = 2.91, p < 0.01) and P300 latencies (t&9) = 3.43, p < 0.01). No effect was observed on NlOO latenties and only a trend was observed on the N200 component latencies (t&9> = 1.5, p < 0.06). Significant effects were observed on the RT minus NlOO interval (t(1,9) = 2.77, p < 0.051, and the RT minus N200 interval (t(1,9) = 2.41, p < 0.051, but not on the RT minus P300 interval. We observed an effect on the interval between N200 and P300 (t(1,9) = 3.32; p < 0.01) but only a trend on the interval N200 minus NlOO (t(1,9) = 1.63, p < 0.09) (Table 1). Significant effects of S-R compatibility have thus been found with RT and P300 latencies (Fig. 0, in accordance with previous results in the

19 (1995) 257-261

259

Effect of compatibility stimulus-response on P3 latency

I

I

I

0

I

200

I

I

I

400

I

600

I

I

I

Fig. 1. Grand average wave forms of S-R compatibility on P300 latencies. Note that a trend is observed latency of the N200 component.

Table 1 S-R compatibility effects on ERP latencies, reaction time and intervals between ERPs peak latencies or between peak latencies. Nl, NlOO peak latencies; N2, N200 peak latencies; P3, P300 peak latencies; RT, reaction time. Nl

ERP latencies Compatibility

Comp. Incomp.

Mean SD Mean SD

Difference TR-Nl

Subtractions Comp.

Mean SD

Incomp.

Mean SD

Difference * p < 0.05. * * p < 0.01. * * * p < 0.001.

255.8 62.9 299 97.1 -43.2 *

N2 128 13.1 124.8 16.9 NS

TR-N2 194.9 80.7 230.2 108.9 -35.1 *

P3 188.8 39.2 193.8 44.7 NS

TR-P3 16.6 98.8 2.2 147.8 NS

P3-N2 178.4 70 228 96.8 ’ -49.6

effects for the

RT and ERPs

RT 367.2 62.7 411.6 92 44.4 *

t

Ins.

800

383.8 53.6 423.8 84 40 * N2-Nl 60.8 37.9 68.8 48.5 NS

J.-L. Nandrino, F.E. Massioui / International Journal of Psychophysiology 19 (199.5) 257-261

260

THEORETICAL SCHEMATA OF COMPATIBILITY S-R EFFECTS

NZ Nl RT

Moreover, the same magnitude of S-R compatibility effects observed on RT (40 ms), on P300 (44.4 ms) and on the interval P300 minus N200 (49 ms) supports the idea that this effect is generated during the N200-P300 interval and by propagation or “pushing effect” it is observed on P300 and on RT. Our results can be related to the interpretation which considers the N200 component as reflecting stimulus classification and pattern recognition (Ritter et al., 1982; Ritter et al., 1983). An S-R compatibility task shows how stimulus analysis and the corresponding motor response processing are closely linked. The response selection, localized in the N200P300 interval argues in favor of the co-activation of sensory and motor systems and supports the idea of an early motor activation before completion of the evaluation process (Coles et al., 1985). Such localization is not in contradiction with the idea that these processes could result from one or more previous processes (Osman et al., 1992) or response channels in terms of Gratton et al. (1988).

----‘“\--rComp.Effect

P3 omp.Effect

I ,

I

NZ-NT

{ Comp.Effect

I TR_P3

I

Fig. 2. Localization of the compatibility S-R effects on the time window between N200 and P300 latencies, as shown from compatibility S-R effects observed on the different ERPs components and on the different time intervals.

literature (Ragot, 1984; Pfefferbaum et al., 1986; Renault et al., 1988; Bashore, 1990; Fiori et al., 1992). This latter result supports the idea that the P300 component is related to response selection processes. This P300 component would correspond to the “P-CR” component described by Falkenstein et al. (1994) as being sensitive to response selection processing. The reasoning based on the effects observed on the peak latencies did not confirm our hypothesis, since we observed only a trend on the N200 component. This suggests that response selection processing, ending with P300, could partially start at around N200. In contrast, the subtraction method allowed us to localize effects that are not identifiable with the former method. The presence of an S-R compatibility effect on the interval RT minus N200 and its absence on the interval RT minus P300 on one hand, and the presence of this effect on the interval P300 minus N200 on the other hand, support the idea that S-R compatibility is processed between N200 and P300 (Fig. 2).

Acknowledgements

The authors wish to thank Dr. Richard Ragot for reading the first draft and Drs. Sabrina Davis and Jim Everett for their helpful assistance in correcting the text.

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