<p> Although nearly one third of the Canadian population is projected to be over the age of
65 by the year 2030, we know relatively little about how aging affects brain function
generally, let alone how aging affects visual perception. The current dissertation was
conducted as part of a research programme designed to better characterize how aging
affects visual perception. </p> <p> Older persons exhibit a variety of deficits for perception of complex visual forms. The
perception of these complex forms-including everyday forms such as faces and
objects-is subserved by low-level channels that are selective, or tuned, for the
orientation and spatial frequency of luminance-defined contours in the visual scene. The
bandwidth of these channels is inversely related to the amount of information that they
can pass on to higher visual processes; narrowly-tuned channels are better. Single-cell
physiological investigations of primates suggest that visual cortex neurons thought to
subserve these channels exhibit broader tuning in senescence. If these channels become
broadly-tuned in older aging, this could explain age-related deficits for complex form
perception. In Chapters 2 and 3 of the current thesis, I measured the tuning of these
channels in otherwise healthy, older humans using psychophysical masking techniques. In
Chapters 4 and 5, I measured the average tuning of the neurons thought to underlie these
channels in older human adults, physiologically, using electroencephalography (EEG).
Despite the aforementioned reports of functional decline in senescent neurons,
psychophysical and physiological orientation and spatial frequency tuning did not differ
between younger and older adults. One explanation for this discrepancy is that there is a
methodological issue in the single-cell primate literature wherein anesthetics interact
with senescence to produce seemingly broader neural tuning. Another explanation is that
older humans do have otherwise detuned neurons and channels, but are able to tune their
neurons and channels by the action of consciousness, attention, or age-related
compensatory brain reorganization. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19175 |
| Date | January 2010 |
| Creators | Govenlock, Stanley |
| Contributors | Bennett, Patrick, Sekuler, Allison, Psychology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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