SPATIAL AND
CHROMATIC PROPERTIES OF NEURONS IN THE VISUAL PATHWAY
Can
neurons represent both the form and colour of surfaces, or are separate
pathways required for these two attributes? We have been studying the
response of neurons in retina and cortex to uniform surface colours and
coloured patterns. We think it likely that early in striate cortex a
separate pathway is formed to code the colour of surfaces, and this
pathway is largely insensitive to spatial form.
CONTRAST, GAIN CONTROLS AND COLOUR IN STRIATE
CORTEX (V1) How
do we determine that a neuron is important for colour vision? We have
explored the hypothesis
that such neurons will retain their colour tuning in the face of
changes in other
attributes of the visual stimulus, such as size, contrast or the type
of spatial pattern.
CONTRAST ADAPTATION EARLY IN THE VISUAL PATHWAY Prolonged
viewing of a simple pattern leads to changes in its appearances, and of
similar patterns. It has long been thought that this reflects the
adaptation of neurons in the visual cortex. We have shown that
adaptation is not confined to visual cortex, but can rather be found
early in the visual pathway, in magnocellular-pathway retinal ganglion
cells.
LINEAR AND NON-LINEAR RECEPTIVE FIELD PROPERTIES
OF VISUAL NEURONS Receptive
fields early in the visual pathway are usually thought to be small and
simple. We have shown that many of them are sensitive to a larger
fraction of visual space than first thought.
