shift invariance

[Norberto Grzywacz]

On Fri, 1 Mar 1996, DeLiang Wang wrote:

> 
> I'd like to know the evidence that the visual system achieves shift
> (translation) invariance (I'd appreciate references if any). It seems
> that the eye "focuses" on the object of interest first. In other
> words, the eye seems to shift with the object, not that the visual system is 
> recognizing the object wherever it occurs on the retina.
> 



A form of shift invariance appears to exist in cortical neurons of the 
anterior part of the superior temporal sulcus and of the inferior temporal 
cortex.  Neurons in these areas have large receptive fields, which can show 
considerable selectivity for what the stimulus is irrespective of exactly 
where it is in the visual field.  I would call this property "selectivity 
shift invariance," to contrast with "absolute shift invariance," which 
the cortex does not appear to have.  The amplitude of cell responses vary 
(fall) with eccentricity, even though they maintain their selectivity.  
Moreover, the amplitude of the responses is modulated by the presence of 
other objects in the receptive fields.

Three relevant references are:

Tovee, M.J., Rolls, E.T., and Azzopardi, P. (1994) Translation invariance
in the responses to faces of single neurons in the temporal visual
cortical areas of the alert macaque.  J. Neurophysiol. 72:1049-1060.

Rolls, E.T. and Tovee, M.J. (1995) The responses of single neurons in the
temporal visual cortical areas of the macaque when more than one stimulus
is present in the receptive field.  Exp. Brain Res. 103:409-420.

Ito, M., Tamura, H., Fujita, I., and Tanaka, K. (1995) Size and position
invariance of neuronal responses in monkey inferotemporal cortex.  J.
Neurophysiol.  73:218-226.




Norberto Grzywacz