Reach tracking reveals dissociable processes underlying cognitive control

Abstract

The current study uses reach tracking to investigate how cognitive control is implemented during online performance of the Stroop task (Experiment 1) and the Eriksen flanker task (Experiment 2). We demonstrate that two of the measures afforded by reach tracking, initiation time and reach curvature, capture distinct patterns of effects that have been linked to dissociable processes underlying cognitive control in electrophysiology and functional neuroimaging research. Our results suggest that initiation time reflects a response threshold adjustment process involving the inhibition of motor output, while reach curvature reflects the degree of co-activation between response alternatives registered by a monitoring process over the course of a trial. In addition to shedding new light on fundamental questions concerning how these processes contribute to the cognitive control of behavior, these results present a framework for future research to investigate how these processes function across different tasks, develop across the lifespan, and differ among individuals.

Keywords: Cognitive control; Flanker task; Reach tracking; Stroop task; Trial sequence effect.

Figure 1

Diagram of experimental setup. A rear-mounted projector was used to display the task on a Plexiglass screen mounted upright on the table in front of the participant.

Figure 2

Average performance on each of the four trial types (cC, iC, cI, iI) for measures of (A) initiation time and (B) curvature. Error bars indicate standard errors.

Figure 3

Average reach trajectories to each target for (A) trials preceded by a congruent trial and (B) trials preceded by an incongruent trial. The color of each line indicates the semantic content of the stimulus presented on that trial (black = “GREEN”, dark grey = “RED”, and light grey = “BLUE”), whereas the location of the target indicates the color of the text presented on that trial (labeled with a “G”, “R”, or “B” for clarity). Responses to congruent trials are presented with solid lines, while responses to incongruent trials are presented with dashed lines.

Figure 4

Distractor attraction scores for iI trials (dashed line) and cI trials (solid line). Movement trajectories were pulled toward the location matching the semantic content of the stimulus for much of the movement on cI trials, reflecting strong competition between the text's meaning and color. However, iI trials showed no attraction, and even some repulsion away from the location corresponding to the semantic content of the stimulus. Shaded area reflects standard error of the mean.

Figure 5

Average performance on each of the four trial types (cC, iC, cI, iI) for measures of (A) initiation time and (B) curvature. Error bars indicate standard errors.

Figure 6

Distractor attraction scores for iI trials (dashed line) and cI trials (solid line) in the flanker task. Movement trajectories for both iI and cI trials were pulled toward the response cued by the misleading flanker letters, indicating strong competition between the two cued responses. However, iI trials showed significantly less attraction to the response cued by the flanker letters than cI trials from 16-18% of the movement.

Figure 7

Average reach trajectories to each target for (A) trials preceded by a congruent trial and (B) trials preceded by an incongruent trial. The color of each line indicates the identity of the flanker letters presented on that trial (black = A's, dark grey = B's, and light grey = K's), while the location of the target indicates the identity of the center letter presented on that trial (labeled with a “A”, “B”, or “K” for clarity). Responses to congruent trials are presented with solid lines, while responses to incongruent trials are presented with dashed lines.

Figure 8

Average performance on each of the four trial types (cC, iC, cI, iI) for measures of (A) initiation time and (B) curvature. Error bars indicate standard errors. Target and distractor repetition trials included in analysis.