Sequential Modulations in a Combined Horizontal and Vertical Simon Task: Is There ERP Evidence for Feature Integration Effects?

Abstract

In the Simon task, participants respond faster when the task-irrelevant stimulus position and the response position are corresponding, for example on the same side, compared to when they have a non-corresponding relation. Interestingly, this Simon effect is reduced after non-corresponding trials. Such sequential effects can be explained in terms of a more focused processing of the relevant stimulus dimension due to increased cognitive control, which transfers from the previous non-corresponding trial (conflict adaptation effects). Alternatively, sequential modulations of the Simon effect can also be due to the degree of trial-to-trial repetitions and alternations of task features, which is confounded with the correspondence sequence (feature integration effects). In the present study, we used a spatially two-dimensional Simon task with vertical response keys to examine the contribution of adaptive cognitive control and feature integration processes to the sequential modulation of the Simon effect. The two-dimensional Simon task creates correspondences in the vertical as well as in the horizontal dimension. A trial-by-trial alternation of the spatial dimension, for example from a vertical to a horizontal stimulus presentation, generates a subset containing no complete repetitions of task features, but only complete alternations and partial repetitions, which are equally distributed over all correspondence sequences. In line with the assumed feature integration effects, we found sequential modulations of the Simon effect only when the spatial dimension repeated. At least for the horizontal dimension, this pattern was confirmed by the parietal P3b, an event-related potential that is assumed to reflect stimulus-response link processes. Contrary to conflict adaptation effects, cognitive control, measured by the fronto-central N2 component of the EEG, was not sequentially modulated. Overall, our data provide behavioral as well as electrophysiological evidence for feature integration effects contributing to sequential modulations of the Simon effect.

Keywords: ERP; Simon task; action control; conflict adaptation; feature integration; sequential modulation.

FIGURE 1

The figure shows different trial sequences of the Simon task with a dimensional repetition (A) and a dimensional change (B). Depicted are different trial types (trial N) following a horizontal corresponding trial (trial N-1). For each trial sequence, degree of event file overlap (complete repetition, partial repetition, complete change) and S–R correspondence sequence (c = corresponding, n = non-corresponding, small letters indicating previous trial characteristics, capital letters current trial characteristics) are indicated. In this example, the upper response key was assigned to the X stimulus and the left hand, whereas the lower key was assigned to the S stimulus and the right hand. The correct response key for each trial is colored in gray.

FIGURE 2

The figure shows the time course of a trial in the two-dimensional Simon task; the example used depicts trials with an X target. For each of the five possible stimulus positions, S–R correspondence (corresponding, non-corresponding, neutral) according to hand positioning and S–R mapping for one of the four counterbalanced groups is indicated (upper key: left hand, X; lower key: right hand, S). The correct response key under these instructions is colored in gray. Frames at the five positions were visible throughout the trial. During target presentation, X or S appeared in one frame while the other frames were filled with noise stimuli (three lateral bars).

FIGURE 3

The figure shows the average RTs as a function of dimensional repetition (left) and dimensional change (right) as well as current and previous S–R correspondence (sequence types: c–C, n–C, c–N, n–N). Error bars indicate the standard error of the mean. h = horizontal dimension, v = vertical dimension, c = corresponding S–R relation, n = non-corresponding S–R relation. Small letters indicate previous trial features, capital letters current trial features of a trial sequence.

FIGURE 4

The figure displays the grand averages at electrode site FCz as a function of dimensional repetition (left panels) and dimensional change (right) as well as the current and previous S–R correspondence sequence (sequence types: c–C, n–C, c–N, n–N). Positive deflections are displayed downward. The gray area highlights the analyzed time-window of the N2 component (200–330 ms). Black lines signal current corresponding trials, gray lines signal current non-corresponding trials. Solid lines indicate previous corresponding and dashed lines indicate previous non-corresponding S–R relations. h = horizontal dimension, v = vertical dimension, c = corresponding, n = non-corresponding S–R relation. Small letters indicate previous trial features, capital letters current trial features of a trial sequence.

FIGURE 5

The figure shows the average peak amplitude of the fronto-central N2 component as a function of corr N (left) and as a function of spat N and spat N-1 (right). Error bars indicate the standard error of the mean. c = corresponding, n = non-corresponding S–R relations.

FIGURE 6

The figure displays the grand averages at electrode site Pz as a function of dimensional repetition (left) and dimensional change (right) and S–R correspondence sequence (sequence types: c–C, n–C, c–N, n–N). Positive deflections are displayed downward. The gray area highlights the analyzed time-window of the P3b component (390–450 ms). Black lines signal current corresponding trials, gray lines signal current non-corresponding trials. Solid lines indicate previous corresponding and dashed lines indicate previous non-corresponding S–R relations. h = horizontal dimension, v = vertical dimension, c = corresponding, n = non-corresponding S–R relations. Small letters indicate previous trial features, capital letters current trial features of a trial sequence.

FIGURE 7

The figure shows the mean amplitude of the parietal P3b as a function of dimensional repetition (left) and dimensional change (right) and current and previous correspondence. Error bars indicate the standard error of the mean. h = horizontal dimension, v = vertical dimension, c = corresponding S–R relation, n = non-corresponding S–R relation. Small letters indicate previous trial features, capital letters current trial features of a trial sequence.