Temporal Dissection of Stimulus-Driven and Task-Driven Processes during Perceptual Decision about 3D SFM Stimuli

Abstract

Analyzing the visual properties of a stimulus, such as its shape or its motion, involves a temporally constrained cascade of processes including sensory integration, attentional selection and perceptual decision. In natural conditions, these processing stages may temporally overlap. In this study, we used a time constrained paradigm designed to segregate these stages, and recorded MEG activity to characterize their cortical correlates.

The experimental sequence comprised a structure-frommotion (SFM) target flanked by pre and post masks, which limited the stimulus-driven processes in time.

The MEG responses were recorded in three perceptual tasks bearing on the presence or absence of the target SFM stimulus, on its direction of motion or on its 3D shape.

Subjects’ responses were delayed to the end of the trials using a random stimulus-response mapping.

The analysis of the evoked magnetic fields reveals temporally non-overlapping responses for stimulus-driven and task-related processes.

Source reconstruction reveals that the occipital, dorsal and ventral stimulus-related areas follow different temporal profiles, The response in IPS slowly rising after the beginning of the activity in the lateral occipital cortex and falling back to the baseline prior the delayed motor response, may reflect accumulating evidence on the presented stimulus leading to a motor response, in line with the results from single cell studies in monkey LIP [1].