# Adaptation of the inferior temporal neurons and efficient visual processing

## TL;DR

This paper reviews how neurons in the inferior temporal cortex adapt to visual stimuli over time, suggesting that this adaptation is a common and essential part of visual processing.

## Contribution

The paper provides a comprehensive review of adaptation mechanisms in IT neurons, linking them to broader concepts like efficient coding and predictive processing.

## Key findings

- Repetition suppression in IT neurons occurs naturally during free viewing without forced fixation.
- Short-term activity modulation in IT neurons may be a default process for visual processing.
- Adaptation phenomena are widespread across the visual system and may relate to efficient and predictive coding.

## Abstract

Numerous studies examining the responses of individual neurons in the inferior temporal (IT) cortex have revealed their characteristics such as two-dimensional or three-dimensional shape tuning, objects, or category selectivity. While these basic selectivities have been studied assuming that their response to stimuli is relatively stable, physiological experiments have revealed that the responsiveness of IT neurons also depends on visual experience. The activity changes of IT neurons occur over various time ranges; among these, repetition suppression (RS), in particular, is robustly observed in IT neurons without any behavioral or task constraints. I observed a similar phenomenon in the ventral visual neurons in macaque monkeys while they engaged in free viewing and actively fixated on one consistent object multiple times. This observation indicates that the phenomenon also occurs in natural situations during which the subject actively views stimuli without forced fixation, suggesting that this phenomenon is an everyday occurrence and widespread across regions of the visual system, making it a default process for visual neurons. Such short-term activity modulation may be a key to understanding the visual system; however, the circuit mechanism and the biological significance of RS remain unclear. Thus, in this review, I summarize the observed modulation types in IT neurons and the known properties of RS. Subsequently, I discuss adaptation in vision, including concepts such as efficient and predictive coding, as well as the relationship between adaptation and psychophysical aftereffects. Finally, I discuss some conceptual implications of this phenomenon as well as the circuit mechanisms and the models that may explain adaptation as a fundamental aspect of visual processing.