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Studies on human visible persistence


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Bowling, Alison Catherine 1981 , 'Studies on human visible persistence', PhD thesis, University of Tasmania.

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The visual system has limited temporal resolution,
with the intensity of brief stimulus presentations being
summed, or integrated over time. This temporal integration
may manifest itself in various ways, including timeintensity
reciprocity at threshold (Bloch's Law), flicker
fusion, some masking phenomena, and visible persistence.
The degree of visual temporal resolution varies with a
number of conditions including luminance, field size, and
the spatial frequency of gratings. Many of these temporal
properties may possibly be explained in terms of interactions
between two parallel visual mechanisms - "sustained" and
"transient" channels. These appear to analyse pattern and
movement respectively. This thesis reports investigations into properties of
one of these temporal characteristics, visible persistence.
It attempts to relate persistence to threshold measures of
temporal summation, especially time-intensity reciprocity.
It is argued that persistence may occur at more than one
level of the visual system and that the more peripheral
component may result from processes similar to those responsible
for the "critical duration" of time-intensity, reciprocity.
Using a separation threshold method, persistence duration
was found to increase with both increasing spatial frequency
and decreasing contrast. By measuring persistence over
several stimulus durations it was possible to show that it
consisted of two components. One occurred only at brief stimulus durations and declined linearly with increasing
stimulus duration. The other appeared to be present and
approximately constant at every stimulus duration. Varying
stimulus conditions such as orientation, contrast and
spatial frequency affected these components differently.
These effects were consistent with the hypothesis that one
component is peripherally located and the other more central.
It was argued that persistence at both levels is due to
the prolonged nature of sustained cell responses, with
high frequency gratings stimulating mechanisms with longer
response durations than the mechanisms stimulated by low
frequency gratings. It was also proposed that response
duration may be influenced by the amplitude or latency of
transient mechanisms but neither flicker adaptation nor
reaction time experiments supported this.
It was noted that the conditions which elevate persistence
such as the use of higher spatial frequencies, oblique
orientations and lower contrast levels would all be expected
to produce weaker neural stimulation. It appears therefore
that for weaker neural stimulation the response duration is
lengthened, as if in compensation.

Item Type: Thesis - PhD
Authors/Creators:Bowling, Alison Catherine
Keywords: Visual perception, Vision, Visual evoked response, Threshold (Perception)
Copyright Holders: The Author
Copyright Information:

Copyright 1981 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.) - University of Tasmania, 1981. Bibliography: l. 226-242

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