Influence of Attention on Neuronal Responses
The effects of exogenous spatial cueing on neuronal responses. Left: In relevant
optic flow trials red, centered fixation is followed by optic flow visual motion with 1 of
8 eccentric radial centers-of-motion and then an 8 spot array requiring a saccade to
the remembered location of the radial center. In irrelevant optic flow trials blue), a
flashed square preceded the optic flow and a saccade was required to the
remembered square location. Right: Precue effects were seen in the irrelevant optic
flow condition by comparing trials in which the precue was nearby (green versus far
from light blue the radial center.
Optic flow selectively activates neurons in medial superior temporal (MST) cortex. We find that many MST neurons yield larger and more selective responses when the optic flow guides a subsequent eye movement. Smaller, less selective responses are seen when optic flow is preceded by a flashed precue that guides eye movements. Selectivity can decrease by a third (32%) after a flashed precue is presented at a peripheral location as a small spot specifying the target location of the eye movement. Smaller decreases in selectivity (18%) occur when the precue is presented centrally with its shape specifying the target location.
Shape precues presented centrally, but not linked to specific target locations, do not appear to alter optic flow selectivity. The effects of spatial precueing can be reversed so that the precue leads to larger and more selective optic flow responses: A flashed precue presented as a distracter before behaviorally relevant optic flow is associated with larger optic flow responses and a 45% increase in selectivity. Together, these findings show that spatial precues can decrease or increase the size and selectivity of optic flow responses depending on the associated behavioral contingencies.
Figure 2: Signal Neuron Responses. Left: Spike density histograms (SDHs) of
responses to 8 radial center stimuli in relevant optic flow red and irrelevant optic
flow blue trials for 1-s optic flow stimulus period (vertical bar = 100 spikes/s). This
neuron prefers the right-upper radial center with larger responses in relevant optic
flow trials red shading). Right: SDHs for the near green and far light blue) precue
trials in a neuron preferring the lowest radial center with larger responses in near
precue trials green shading. Behavioral task effects were concentrated in the first
300 ms of the neuronal responses.
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