Sensitivity to Timing and Order in Human Visual Cortex

TL;DR

This study shows that the human ventral visual stream is highly sensitive to millisecond differences in the timing and order of visual stimuli, influencing object recognition and suggesting timing as a coding mechanism.

Contribution

It provides direct intracranial evidence that fine temporal differences and order in visual stimuli significantly affect neural representations in the human ventral stream.

Findings

Responses are sensitive to timing differences as small as 17 ms.

Order of stimulus presentation strongly influences neural responses.

Timing and order may serve as neural coding mechanisms in visual recognition.

Abstract

Visual recognition takes a small fraction of a second and relies on the cascade of signals along the ventral visual stream. Given the rapid path through multiple processing steps between photoreceptors and higher visual areas, information must progress from stage to stage very quickly. This rapid progression of information suggests that fine temporal details of the neural response may be important to the how the brain encodes visual signals. We investigated how changes in the relative timing of incoming visual stimulation affect the representation of object information by recording intracranial field potentials along the human ventral visual stream while subjects recognized objects whose parts were presented with varying asynchrony. Visual responses along the ventral stream were sensitive to timing differences between parts as small as 17 ms. In particular, there was a strong dependency on the temporal order of stimulus presentation, even at short asynchronies. This sensitivity to the order of stimulus presentation provides evidence that the brain may use differences in relative timing as a means of representing information.