College3vraag15

Wat zegt het experiment van Motter (1994) over het rol van topografische (retinotope) representaties in de interactie tussen feedforward netwerken en feedback netwerken in visuele perceptie?

Antwoord:
Motter presented a circular array of
objects (oriented bars) around a fixation spot. The color of the fixation spot
was used as a cue. The color of half of the objects in the
array matched the color of the cue. Single neuron
activity was recorded in area V4 during a discrimination
task based on the color of the cue. The initial activity of
V4 cells was the same for cells responding to the
matching color and for cells responding to the nonmatching
color. But 150–200 msec after stimulus onset
the cells that responded to the color of the cue showed
enhanced activity. In contrast, the activity of cells responding
to the nonmatching color was attenuated. In
this way, ’ ’the topographic representation of the neural
activity in area V4 highlights the potential targets in the
visual scene at the expense of background objects’ ’ A dramatic effect was observed when the color of the
cue switched in the middle of a trial from one alternative
to the other. Following the cue switch, a reversal of
activity occurred during the trial. The activity of the
initially nonmatching cells increased to the level of the
initially matching cells, whereas the activity of the initially
matching cells declined to the level of the initially
nonmatching cells (Motter, 1994b).
The simulations of the model show that
information about the location of an identified object
(target) in an object array can be retrieved by an
interaction in the retinotopic areas of the ventral stream
between a feedback network that carries information
about the identity of the target and a feedforward network
that carries information about the object array
(stimulus). In this way, the ventral stream can select an
object so that the dorsal stream can generate a goaldirected
action

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