Smith, Andrew Timothy (1979) The stimulus specificities of different components of pattern-onset visual evoked potentials in man. Doctoral thesis, Keele University.

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The transient visual evoked potential elicited by the onset of a briefly presented pattern typically contains three major components occurring within 200ms of stimulus onset. The first of these, Cl, is believed to originate in striate cortex, while the second, CII, and the third, Cl11, are thought to originate in separate regions of prestriate cortex.
In this thesis a series of experiments 1s presented in which the sensitivity of the sources of these components to the orientation, size, colour and depth of a stimulus pattern is examined.
The amplitude of Cl, the only component which can be reliably elicited by a grating stimulus, varies as a function of the orientation of a previously presented adaptation grating. Attenuation is maximal when the adaptation and stimulus gratings have the same orientation, and decreases as a function of the difference in orientation between the two. The Cl amplitude elicited by a grating in the absence of an adaptation pattern is independent of the orientation of the grating.
The amplitude of all three components elicited by a checkerboard stimulus varies as a function of the periodicity of the checkerboard. Amplitude is maximal at 2.0 cycles/deg and declines with higher or lower periodicities. These sensitivity functions are skewed, amplitude declining more rapidly with high periodicities than with low. The amplitudes of Cl and CII elicited by an invariant checkerboard of optimal size are also sensitive to the periodicity of a previously presented adaptation checkerboard. Attenuation is maximal when the adaptation and stimulus patterns are identical, but amplitude is almost unaffected by adaptation to a checkerboard differing in periodicity from the stimulus by 1.5 octaves. Similar functions were obtained for Cl when a grating adaptation pattern was used, and when a grating stimulus pattern was used 1n conjunction with either a grating or a checkerboard adaptation pattern. CII, elicited by a checkerboard, is unaffected by adaptation to a grating of whatever periodicity. ClII, elicited by a checkerboard, shows no specificity to the periodicity of either a grating or a checkerboard adaptation pattern.
Greater attenuation of the Cl amplitude elicited by a vertical grating occurs following adaptation to a checkerboard with oblique check sides than to one with vertical check sides, and greater attenuation of Cl elicited by a checkerboard with vertical check sides occurs following adaptation to an oblique grating than to a vertical grating. This suggests that Cl is sensitive to the orientations of the fundamental Fourier components of a pattern, rather than to the edges contained in the pattern.
Size specific attenuation of Cl and CII transfers interocularly. Interocular transfer is almost total in the case of CII, but partial in the case of Cl, suggesting a difference in binocularity between striate and prestriate cortex.
Neither Cl nor CII shows specificity to either the colour or the stereoscopic depth of an adaptation pattern.
The significance of these findings in relation to animal single unit studies and human psychophysics is discussed.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry
Divisions: Faculty of Natural Sciences > School of Life Sciences
Depositing User: Lisa Bailey
Date Deposited: 03 Oct 2019 08:07
Last Modified: 03 Oct 2019 08:07

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