Biomedical subjects

P M Grove

Publications and source records attributed to P M Grove.

3 recordsLinked to original sources

PubMed2002

Spatial frequency discrimination in cyclopean vision.

It is well known that inspecting a cyclopean grating causes threshold for detecting a subsequently presented test cyclopean grating to be elevated, and that the threshold elevation is greatest at the adapting frequency. We report here that spatial frequency discrimination threshold is also elevated, but the elevation is greatest at frequencies offset from the adapting frequency, and the elevation at the adapting frequency is near-zero. We conclude that discrimination threshold is determined by the relative activity of cyclopean frequency-tuned channels, and suggest that relative activity is computed at an opponent-frequency stage. Discrimination threshold for cyclopean gratings was 2.5-4% for two observers, and remained approximately constant over the range 0.16-2.0 cycles/ degrees. Discrimination threshold for luminance-defined gratings was only slightly lower. Discrimination threshold was approximately independent of the grating's peak-to-peak disparity over a range of 45:1 for one observer and 17:1 for another. This finding as well as the low value of discrimination threshold are consistent with an opponent-process model. The dot density of every cyclopean grating used was chosen bearing in mind our finding that three or more spatial samples per grating cycle are required before sampling effects can be ignored.

Adult↗

PubMed2001

The backward inclination of a surface defined by empirical corresponding points.

Three experiments were conducted to investigate whether a locus of binocular correspondence extends eccentrically from the vertical horopter. In experiment 1, we investigated whether the backward inclination of the vertical horopter was manifested in the angle at which readers prefer to orient the page. All observers preferred a page inclined backwards to any other orientation. This backward inclination was less than predicted from previous psychophysical reports, however. In experiment 2, we investigated the extent of binocular correspondence, defined by minimal apparent interocular horizontal motion, in the central 24 deg of the binocular field. Our data define a planar surface inclined top-away from the observer as a locus from which psychophysical corresponding points are stimulated. In experiment 3, we measured vertical adjustments required to eliminate apparent vertical motion. Together, the pattern of results from experiments 2 and 3 is most consistent with a planar surface, inclined top-away from the observer. This is consistent with Helmholtz's account of the backward inclination of the vertical horopter and expands the locus of zero horizontal disparity from a single line in the median plane to eccentric loci extending at least +/- 12 deg in the central binocular field.

Humans↗

PubMed1999

Ecologically invalid monocular texture leads to longer perceptual latencies in random-dot stereograms.

Two experiments were conducted to explore Gillam and Borsting's (1988, Perception 17 603-608) report that uncorrelated monocular texture facilitates stereopsis by shortening the latency to see depth in random-dot stereograms. Experiment 1 used stereograms similar, in pattern but not disparity, to Gillam and Borsting's with monocular texture present or absent. A third condition, where monocular texture was dissimilar to the binocular panels and background, was also used. We were unable to generalize the findings of Gillam and Borsting for a depth step of 6 min of arc to a larger depth step of 24 min of arc. That is, we observed no significant difference in latencies between the conditions with monocular texture absent and present at a disparity of 24 min of arc. We found latencies to be significantly longer in the monocular-texture-different condition than the monocular-texture-absent condition, however. We account for this, ad hoc, by arguing that the monocular-texture-different stereogram depicts a rare or 'accidental' visual scenario. This account was supported by the results of experiment 2 which showed that stereograms depicting accidental views yielded longer latencies than those depicting generic views. We conclude that the ecological validity of monocular texture must also be considered when assessing the effects of monocular texture on stereopsis.

Depth Perception↗