Axis-of-Motion Affects Direction Discrimination, Not Speed
Discrimination
Nestor Matthews and Ning Qian, Vision Research 1999,
39:2205-2211.
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(PDF file, 0.21MB)
Abstract
The motion of an object can be described by a single velocity vector,
or equivalently, by direction and speed separately. Similarly, our
ability to see subtle differences in the motion of two objects could
be constrained by either a velocity-based sensory response, or
separate sensory responses to direction and speed. To distinguish
between these possibilities we investigated whether direction
discrimination and speed discrimination were differentially affected
by changes in the axis-of-motion. Psychophysical data from 12 naive
observers indicated that direction discrimination depended on
axis-of-motion, but speed discrimination did not. The difference
suggests that a velocity-based sensory response is not the limiting
factor on the two tasks. Instead, the results imply that the sensory
response which constrains speed discrimination is at least partially
independent from the sensory response which constrains direction
discrimination.
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