Abstract
Neural responses in many visual areas are usually reduced when repeating a visual stimulus. This adaptation or repetition suppression effect has recently aroused considerable interest because of the use of fMRI-adaptation to infer stimulus selectivities or invariances of neuronal populations in humans. The use of fMRI-adaptation necessitates an understanding of the mechanisms of adaptation. Given the increased use of fMRI-adaptation, we believe it is time to review our current understanding of the mechanisms of adaptation and their implications for the interpretation of functional imaging adaptation data. In the proposed symposium we will discuss experiments and computational work that provided new insights into the neural mechanisms of adaptation. Importantly, we will compare adaptation mechanisms in different visual areas in non-human and human primates. In addition, we will address adaptation effects of different neural measures, i.e. spiking activity, local field potentials and fMRI, and integrate these experimental data with recent computational work. We will have 4 speakers, giving each 30-minute talks (including 5 minutes of discussion time). Adam Kohn (Albert Einstein College of Medicine) will present his recent work on adaptation mechanisms in macaque primary visual cortex using microelectrode array recordings of populations of single neurons. These new data on orientation tuning and contrast sensitivity demonstrate a rich variety of adaptation effects which can be explained by a simple computational model, reconciling previous findings of effects of adaptation on tuning in areas V1 and MT. The second speaker, Rufin Vogels (K.U. Leuven), will review the effects of adaptation on the shape tuning of macaque inferior temporal cortex. He will compare adaptation effects of spiking activity and local field potentials (LFPs) and test predictions of different models of adaptation. The spiking activity and LFPs adaptation data agreed with input-dependent, but not response-dependent neural fatigue models. Kalanit Grill-Spector (Stanford University) will examine different models of adaptation using high-resolution fMRI in human ventral temporal cortex. She will compare adaptation effects in different ventral regions and across different adaptation paradigms in relation to predictions from different neural models of adaptation. These fMRI data suggest that different adaptation mechanisms underlie fMRI-adaptation in different brain regions and may differ between paradigms. The fourth speaker, Stephen Gotts (NIMH), will review computational work on adaptation mechanisms and relate these to physiological work in the macaque and human MEG and intracranial EEG recordings. This work suggests the need to consider synchronization of neural activity in addition to changes in the response level. It also links the behavioral improvement in performance with repetition to neural adaptation mechanisms.
The multi-region and multi-technique approach makes the proposed symposium rather unique and original. The symposium is of obvious interest to visual neuroscientists -students and faculty – and given the link between neural adaptation and perceptual aftereffects and repetition priming, this topic will also be of interest to visual psychophysicists. The attendees will gain insights into mechanisms of adaptation, which are crucial for interpreting fMRI-adaptation results and linking these with behavioral effects of stimulus repetition.