Biomedical subjects

E L Cameron

Publications and source records attributed to E L Cameron.

4 recordsLinked to original sources

PubMed2001

Stimulus probability directs spatial attention: an enhancement of sensitivity in humans and monkeys.

We examined whether improvements in sensory processing, defined as changes in sensitivity, could be elicited in a simple luminance discrimination task without eliciting concomitant changes in decision processing. To this end we developed a task, for use in both humans and monkeys, in which prior knowledge about where a discriminative stimulus was likely to appear (1) offered no decisional advantage in solving our task and (2) could be parametrically varied to yield a psychometric function. We found that if we parametrically varied the quality of prior knowledge, by increasing the probability, and thus the certainty, that a discriminative stimulus would appear at a particular location under these conditions, luminance discrimination improved for both human and monkey subjects. This improvement was correlated with an enhancement in sensory processing, but not with any systematic changes in decisional processing, as assessed by signal detection theory. These results suggest that (1) sensory processing and decision processing can be separated by task design and (2) systematic changes in prior knowledge about where a stimulus may appear can lead to systematic changes in sensitivity; providing a psychometric function for the influence of prior knowledge on perceptual sensitivity. Importantly, these results were obtained from both human and monkey subjects. Similar task designs could be used in physiological studies attempting to generate linking hypotheses between psychometric and neurometric functions, ultimately allowing changes in perceptual sensitivity to be linked to changes in an underlying neural substrate.

Adult↗

PubMed2001

Characterizing visual performance fields: effects of transient covert attention, spatial frequency, eccentricity, task and set size.

We investigated whether transient covert attention would differentially affect 'performance fields' (shape depicted by percent correct performance at particular locations in the visual field) for orientation discrimination, detection and localization tasks, while manipulating a number of visual factors. We found that although attention improved overall performance, it did not affect performance fields. Two patterns were observed regardless of the presence of a local post-mask, the stimulus orientation, or the task. A horizontal-vertical anisotropy (HVA) became more pronounced as spatial frequency, eccentricity and set size increased. A vertical meridian asymmetry (VMA) became more pronounced as spatial frequency and eccentricity increased. We conclude that performance fields are determined by visual, rather than by transient attentional, constraints.

Analysis of Variance↗

PubMed1992

Spatial frequency selective mechanisms underlying the motion aftereffect.

The motion aftereffect (MAE) was used to study the spatial frequency selectivity of suprathreshold motion perception. Observers were adapted to drifting sine-wave gratings confined to a retinal eccentricity of approx. 4 deg. The magnitude of the subsequent MAE was measured while viewing a stationary sine-wave grating test surface of one of a number of spatial frequencies. The largest MAE was found when the spatial frequency of the test stimulus was the same as that of the adapting stimulus. This phenomenon held for spatial frequencies between 0.5 and 4 c/deg, and was robust with changes in contrast of either adapting or test gratings. However, at an adapting spatial frequency of 0.25 c/deg, the peak MAE was observed at 0.5 c/deg. Control experiments indicated that this peak shift was not the result of the reduced number of cycles in the stimulus, nor the temporal frequency. There was no measurable MAE at spatial frequencies lower than 0.25 c/deg. These results suggest the existence of a "lowest adaptable channel" for the motion aftereffect.

Adaptation, Ocular↗

PubMed1990

Adaptation to tilt is not produced by eye-muscle potentiation.

The role of eye-muscle potentiation in adaptation to prismatic tilt was evaluated by assessing the presence of cyclotorsion induced by prolonged wearing of tilting prisms. Fundus photographs, containing the retinal image of the test line adjusted to the subjective vertical, were obtained before and after prism viewing that induced a 6 degrees aftereffect. The angular separation of the retinal images of the test line between pre- and post-prism photographs matched, in all cases, the difference in orientation between pre- and post-prism adjustment of the test line to the vertical. The data, therefore, clearly show that the eye is in exactly the same orbital position before and after substantial tilt aftereffects are induced. These results argue against the eye-muscle potentiation explanation of tilt aftereffects, that is, the explanation which says that tilt aftereffects are the result of prism induced changes in cyclotorsion.

Adaptation, Ocular↗