Trevor John Hine

Detection mechanisms in L-, M-, and S-cone contrast space

Detection thresholds were obtained for a 2 degrees Gaussian-blurred spot flashed for 200 ms on an 8.9 degrees white adapting field of 1070 trolands. The spots contrast was represented in an L-, M-, and S-cone contrast space. Detection thresholds were obtained for many vectors close to specific but theoretically important planes within this space. A three-dimensional surface was fitted to the data generated by the probability summation of three mechanisms, each a weighted sum of cone contrasts. The fit revealed a red-green chromatic mechanism driven by delta L/L--delta M/M with no S-cone input that was 1 order of magnitude more sensitive than the two other mechanisms. The latter consisted of a luminance mechanism with little S-cone input and a blue-yellow chromatic mechanism with the S cone opposed to L and M cones.

Cognitive and gender factors influencing navigation in a virtual environment

Virtual environments (VEs) are becoming popular as media for training, modelling and entertainment. Little is known, however, about the factors that affect efficient and rapid acquisition of knowledge using this technology. Five experiments examined the influence of gender, passive/active navigation, cognitive style, hemispheric activation measured by electroencephalography and display information on the acquisition of two types of navigational knowledge using a VE: route and survey knowledge. Males acquired route knowledge from landmarks faster than females. In situations where survey knowledge must be used, proficiency in visual-spatial cognition is associated with better performance. The right cerebral hemisphere appears to be more activated than the left during navigational learning in a VE. In identifying cognitive factors that influence VE navigation, these results have a number of implications in the use of VEs for training purposes and may assist in linking processes involved in navigation to a more general framework of visual-spatial processing and mental imagery.

Computation of cone contrasts for color vision research

Cone-contrast coordinates have proved useful for representing transient test stimuli used in color vision experiments. These representations automatically take into account the spectral absorption of cones and any Weberian adaptation to steady fields of light. Under these conditions, they also can be interpreted as being an approximation to the incremental cone response. A detailed methodology is presented for making appropriate measurements and calculations of cons contrasts for any light source, especially color monitors.

The use of virtual reality in acrophobia research and treatment.

Acrophobia, or fear of heights, is a widespread and debilitating anxiety disorder affecting perhaps 1 in 20 adults. Virtual reality (VR) technology has been used in the psychological treatment of acrophobia since 1995, and has come to dominate the treatment of numerous anxiety disorders. It is now known that virtual reality exposure therapy (VRET) regimens are highly effective for acrophobia treatment. This paper reviews current theoretical understanding of acrophobia as well as the evolution of its common treatments from the traditional exposure therapies to the most recent virtually guided ones. In particular, the review focuses on recent innovations in the use of VR technology and discusses the benefits it may offer for examining the underlying causes of the disorder, allowing for the systematic assessment of interrelated factors such as the visual, vestibular and postural control systems.

The Effects of Visual Discomfort and Pattern Structure on Visual Search

Unpleasant somatic and perceptual side effects can be induced when viewing striped repetitive patterns, such as a square wave or a page of text. This sensitivity is greater in participants with higher scores on a scale of visual discomfort. In three experiments the effect that this sensitivity has on performance efficiency in a reading-like visual search task was investigated. In experiments 1 and 2, the ‘global’ structure of the patterns was manipulated to produce a square-wave, a checkerboard, and a plaid pattern. It was found that the group that suffered severe visual discomfort took significantly longer than other groups to perform the task, with interference greatest with presentation of the square-wave-like pattern. This supports the prediction of greatest distraction of visual attention from the local target elements with presentation of the pattern structure inducing greatest visual discomfort. In experiment 3, the internal pattern components were manipulated and task difficulty reduced. A no-interference and two interference patterns, one with a global characteristic only and the second made up of distracting line elements, containing global and local components were used. The global pattern structure produced interference effects on the visual-search task. All groups performed with the same speed and accuracy on the task involving the no-interference pattern, a finding attributed to reduced task difficulty McConkie and Zolas model of visual attention was used to explain these results.

Texture segregation with luminance and chromatic contrast

Preattentive texture discrimination was investigated using low spatial frequency texture elements. The contrast between the texture elements and the background was either purely luminance or purely chromatic, or some combination of both these types of contrast. The threshold to discriminate correctly the location of a different textured region was obtained from each subject, as was each subjects threshold to detect the elements of the texture. Using the ratio of texture to element detection as a measure of the effectiveness of texture discrimination, little difference could be found between the perception of luminance or chromatic texture. However, there were large and significant variations among subjects with otherwise normal colour vision.

Motion processing deficits in migraine are related to contrast sensitivity

Background: There are conflicting reports concerning the ability of people with migraine to detect and discriminate visual motion. Previous studies used different displays and none adequately assessed other parameters that could affect performance, such as those that could indicate precortical dysfunction. Methods: Motion-direction detection, discrimination and relative motion thresholds were compared from participants with and without migraine. Potentially relevant visual covariates were included (contrast sensitivity; acuity; stereopsis; visual discomfort, stress, triggers; dyslexia). Results: For each task, migraine participants were less accurate than a control group and had impaired contrast sensitivity, greater visual discomfort, visual stress and visual triggers. Only contrast sensitivity correlated with performance on each motion task; it also mediated performance. Conclusions: Impaired performance on certain motion tasks can be attributed to impaired contrast sensitivity early in the visual system rather than a deficit in cortical motion processing per se. There were, however, additional differences for global and relative motion thresholds embedded in noise, suggesting changes in extrastriate cortex in migraine. Tasks to study the effects of noise on performance at different levels of the visual system and across modalities are recommended. A battery of standard visual tests should be included in any future work on the visual system and migraine.

The influence of pattern interference on performance in migraine and visual discomfort groups

Performance in migraine with and without visual aura, non-specific headache and headache-free control groups was measured using a visual search task. Data from groups with high and low visual discomfort were also gathered. No pattern, 2 c/deg, 15 c/deg and a grey field were used in different background conditions. Presentation of patterned backgrounds slowed performance for all groups with the 2 c/deg pattern producing greatest interference. Performance of headache groups did not differ from that of the control group in any condition. The high visual discomfort group responded significantly more slowly than other groups with the 2 c/deg background. It was concluded that the presence of visual discomfort, reported on an everyday basis was a better indicator of heightened sensory sensitivity than the occurrence of migraine with or without aura.

The Ouchi illusion: An anomaly in the perception of rigid motion for limited spatial frequencies and angles

The spatial parameters underlying a novel illusion of relative motion are characterized. A simple stimulus composed of two sine-wave gratings was sufficient to generate the illusion. We measured the response of subjects to rapid, small-amplitude oscillations of this stimulus behind a fixation point. The effect was clearly strongest for acute angles between the gratings, but only when spatial frequency was between 6 and 11 cpd. We surmise that activity in the grating cells of the primate visual cortex (von der Heydt, Peterhans, & Dursteler, 1992) might be the cause of the illusion. The illusion is potentially an important tool in understanding how higher cortical areas combine disparate motion signals.

Estimation of linear detection mechanisms for stimuli of medium spatial frequency

Detection thresholds were obtained for a circularly-symmetric Gabor profile and Craik-Cornsweet profiles presented on a large white adapting field. These stimuli possessed peak spatial power between 1 and 6 c/deg. Their contrast was represented in an L, M and S cone contrast space. Detection thresholds were obtained for many vectors close to specific but theoretically important planes within this space. These data were fitted with a model comprising independent mechanisms, each a weighted sum of cone contrasts. The fit revealed a chromatic mechanism driven by delta L/L-delta M/M with no S cone input. Within cone contrast space, this mechanism was more sensitive than both a luminance mechanism with little S cone input but considerable variation in relative L to M cone input, and a blue-yellow chromatic mechanism.