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Abstract:
Much of the output from the retina does not project to the
visual cortex, but forms the phylogenetically older retinotectal
pathway. One subcortical destination is the superior colliculus,
SC, which is especially implicated in involuntary orienting of
attention and the initiation of eye-movements. The SC is thought to
receive no projections from short-wave sensitive cones (S cones),
but we here show that peripheral stimuli visible only to S cones
elicit normal involuntary attentional effects on responses to
subsequent targets. We can therefore conclude one of two things,
both contrary to current belief: either involuntary attentional
shifts do not require signals in the direct collicular pathway, or
else this retinotectal pathway does in fact include projections
from S cones. Our arguments apply equally to the alternative theory
that attentional capture is driven by signals in the magnocellular
division of the geniculo-striate pathway: this channel is also
thought to be devoid of S cone input. To select stimuli that that
are visible only to S cones, we exploited the phenomenon of
transient tritanopia: our method may be generally useful whenever
the cardinal axes of color space must be determined for individual
observers and at particular retinal positions.
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