Defiitions of some vision key terms and Past paper questions with brief model answers in bullet points
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Vak
Active Vision
Instelling
Cardiff University (CF)
A basic overview of some questions asked by my peers on the topics of vision during movement. A couple of past paper questions with some bullet point answers given by my lecturer.
Negative feedback loop- in order to work out whether you’re pursuing
something accurately, the visual system has to identify the target that you’re
pursuing, then you need to monitor the motion of that target in the image. If the
motion is zero that must mean that the eye is currently following it. Muscles
fatigue, so there is some error, meaning that over the course of time, the target
that you're following will fall off the fovea an this means its moving on the retina.
Zero always means that you're accurate, feedback loop because it is feedback
about the eyes motion that has feedback from the retina about how you're doing,
and loop because you're doing it continuously. (Central heating theory- it is
essentially a thermostat).
The muscles work based on motor commands, retinal motion is coded early on in
the visual system and this can be passed on to the visual system. Need a motor
signal, need eye muscles, need a box that takes information directly from the
retina or other pathways, then build into that box a negative feedback loop.
Negative feedback loop feedbacks into the motor system.
Gain- what goes in comes out (1), what goes in doesn’t fully come out (<1), what
goes in comes out more (>1). It is a generic term.
Threshold elevation- threshold elevation means, in effect, you get less sensitive -
it simply means that a threshold increased between condition B and condition A
so for saccadic suppression, A = substantially before (or after) the saccade and B
= during it. The thresholds that we discussed most in the saccade lecture were
contrasts thresholds - ie the amount of contrast you need to just detect a grating.
So during the saccade, you need more contrast to reach threshold. Thresholds
are rather arbitrary methods wise - one classic definition is that it equals the
contrast that achieves 75% correct. But there are plenty of other definitions. In
the end, that doesn't matter, what matters is whether they go up or down
between condition A and B, however defined.
Prior expectations- an expectation that changes your responses. Produced
through learning. Bayesian theory of learning (see Bayesian lecture).
The eyes have been found to respond to prediction and we have knowledge
about objects and motion. Most objects move but do not change speed very
rapidly. Have predictions and knowledge about how objects tend to move,
therefore, make assumptions about how the pursued object is moved.
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