[visionlist] lecture Keiji Tanaka 12 May 2011

[Tini Eikelboom]

COLLOQUIUM

Op het Nederlands Instituut voor Neurowetenschappen wordt deze week het volgende 
colloquium gehouden:

donderdag 12 mei 2011 om 16:00 uur

Representation of object categories by population of inferotemporal neurons
Keiji Tanaka
RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan

locatie: colloquiumzaal NIN, Meibergdreef 47, Amsterdam
gastheer: Pieter Roelfsema

Abstract

Representation of object categories by population of inferotemporal neurons

Keiji Tanaka
RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan

   The inferotemporal cortex (IT) of the monkey brain is the final stage of the ventral visual 
pathway, which is thought to be responsible for visual object recognition. Because our 
visual recognition is categorical in nature, object categories may be represented in IT and 
earlier stages. However, by carefully determining the stimulus selectivity of individual cells in 
the monkey IT, we previously found that single IT cells' selectivity was determined by 
moderately complex features. The features to which they responded were not abstract 
enough to indicate object categories. A remaining possibility is that object categories are 
represented by the response pattern of a population of IT cells. By recording responses of 
many IT cells to a fixed set of 1084 object images, we examined this possibility. Responses 
of only one or two cells were tested at a time, but by repeating the recording for several 
months in two monkeys, we obtained responses of 674 cells to the stimulus set. By seeing 
the response table from the stimulus side, we can analyze the response pattern evoked by 
each of the stimuli over the 674 cells. We found that two stimuli belonging to the same 
category tended to evoke similar response patterns whereas those belonging to distant 
categories evoked different response patterns. When the 1084 objects were plotted 
according to the dissimilarity of response patterns, objects of the same category clustered. 
Even the hierarchical structure of object categories appeared there. Thus, although the 
stimulus selectivity of individual IT cells is determined in the domain of moderately complex 
features, which is still physical, by having multiple cells with selectivity for various features, 
responses of a population of IT cells represent object categories, which is semantic.
   We are now re-examining the nature of local clustering of cells in the monkey IT. We 
previously found that cells responding to similar features clustered in a columnar local 
region in monkey IT. Is the local clustering of cells in monkey IT determined only in the 
domain of features? Since animals care about object categories rather than features, the 
local clustering of cells may be organized toward the representation of object categories. 
More concretely, we ask whether there are multiple groups of cells responding to different 
features yet associated with the same object categories in a local IT region. To record many 
(~50) cells in a local region, we have developed a technique for chronic recordings with an 
electrode that remains in the brain for a few weeks and is advanced day by day. Responses 
of recorded cells were examined with a fixed set of 850 object images (50 images each for 
17 object categories). Most pairs of cells recorded from a local IT region showed similar 
categorical selectivity. When we examined their responses to the members of their 
commonly effective object category, whereas many of the pairs also had similar selectivity, 
others showed no similar or even complimentary selectivity. These results suggest that 
multiple groups of cells responding to different features yet associated with the same object 
categories cluster in a local IT region.


Tini Eikelboom
secretariat
Netherlands Institute for Neuroscience (NIN)
Meibergdreef 47
1105 BA Amsterdam
The Netherlands
tel  + 31 20 566 4587
fax + 31 20 566 6121
www.nin.knaw.nl
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