Effect of adapter duration on repetition suppression in inferior temporal cortex

Abstract

Many inferior temporal (IT) cortical neurons reduce their response when a stimulus is repeated. Proposed mechanisms underlying this repetition suppression range from “fatigue” to top-down expectations of repetition. Here we examine a prediction from simple fatigue-based models of adaptation: prolonging adapter duration will increase the adapter response, leading to more repetition suppression. To test this, we varied adapter duration from 300 to 3000 ms, keeping the test stimulus duration constant. We observed no effect of adapter duration on repetition suppression when averaging responses across the test presentation. This was not because of a ceiling effect, since repeated presentations of a short adapter increased repetition suppression. Examination of test stimulus responses showed increased repetition suppression with longer adapter durations during the initial response phase, which reversed at a later phase. Across neurons, we found that the degree of repetition suppression covaried with the ratio of the response during the initial transient and later sustained phase of the response during the long adapter presentation, suggesting overlapping mechanisms that underlie adaptation during the adapter and the delayed test. We propose a fatigue-based account in which fatigue increases non-linearly with adapter duration to explain these unexpected findings.

Adaptation aftereffects reveal representations for encoding of contingent social actions

“…Specifically, behavioral adaptation can selectively target the neural mechanisms and tuning characteristics of perceptual processes across the cortical hierarchy ( 1 – 4 ). The inference about the neural mechanisms from the behavioral adaptation is grounded in electrophysiological studies showing how repetitive sensory stimulation results in a transient response decrease in the neuronal populations involved in the processing of the stimulus ( 5 – 12 ). As a behavioral consequence of this neural mechanism, the perception of a subsequently presented ambiguous test stimulus is altered for a short period.…”

The impact of stimulus size and orientation on individual face coding in monkey face-selective cortex

“…We surgically implanted a plastic recording chamber in both monkeys that targeted ML and isolated 882 single neurons in total, using epoxylite-insulated tungsten microelectrodes (FHC) and standard electrophysiological procedures described in detail elsewhere 4 , 16 , 17 , 22 , 23 , 31 , 33 – 38 . Online isolation of single neuron activity was achieved using a level and time threshold (for more details see 22 , 23 , 35 ).…”

GABAergic and cholinergic modulation of repetition suppression in inferior temporal cortex

“…Details about implants and surgery can be found in 34 and will only be briefly summarized here. The placement of the plastic recording chamber was guided with a preoperative magnetic resonance imaging (MRI) scan and verified with MRI scans obtained postoperatively before and in-between recording sessions.…”

“…We employed a stimulus set identical to that used in some of our previous studies on adaptation in macaque IT 34 . The stimulus set consisted of 52 color images of 26 object classes (2 images per class) including human and monkey faces, human and monkey bodies, mammals, birds, fish, snakes, insects, trees, fruits, fractals and manmade objects.…”