Clinical psychophysics

The Random Step Method for Measuring the Point of Subjective Equality

Points of Subjective Equality (PSE) are commonly measured using staircase or constant stimuli methods. However, the staircase method is highly dependent on the step size, and the constant stimuli method is time-consuming. Thus, we wanted to develop an efficient and quick method to estimate both the PSE and the slope of the psychometric function. We developed a random-step algorithm in which a one-up-one-down rule is followed but with a random step size in a pre-defined range of test levels. Each stimulus would be chosen depending on the previous response of the subject. If the subject responded "up", any random level in the lower range would be picked for the next trial. And if the subject responded "down", any random level in the upper range would be picked for the next trial. This procedure would result in a bell-shaped distribution of the test levels around the estimated PSE, while a substantial amount of trials would still be dispersed at both bounds of the range. We then compared this method with traditional constant stimuli procedure on a task based on the Pulfrich phenomenon while the PSEs of participants could be varied using different neutral density filters. Our random-step method provided robust estimates of both the PSE and the slope under various noise levels with small trial counts, and we observed a significant correlation between the PSEs obtained with the two methods. The random-step method is an efficient way to measure the full psychometric function when testing time is critical, such as in clinical settings.

A review of experimental task design in psychophysical eye tracking research

While eye tracking is a technique commonly used in the experimental study of higher-level perceptual processes such as visual search, working memory, reading, and scene exploration, its use for the quantification of basic visual functions (visual acuity, contrast sensitivity, color vision, motion detection) is less explored. The use of eye movement features as dependent variables in a psychophysical investigation can serve multiple roles. They can be central in studies with neurological patients or infants that cannot comply with verbal instructions, understand task demands, and/or emit manual responses. The technique may also serve a complementary role, determining the conditions under which a manual or verbal response is given, such as stimulus position in the visual field, or it can afford the analysis of new dependent variables, such as the time interval between oculomotor and manual responses. Our objective is to review the literature that applied the eye tracking technique to psychophysical problems. The two questions our review raises are: can eye movements (reflex or voluntary) be an objective index of stimulus detection in psychophysical tasks? If so, under what conditions, and how does it compare with traditional paradigms requiring manual responses? Our (non-systematic) methodological review selected studies that used video-oculography as the technique of choice and had a basic visual function as their primary object of investigation. Studies satisfying those criteria were then categorized into four broad classes reflecting their main research interest: (1) stimulus detection and threshold estimation, (2) the effects of stimulus properties on fixational eye movements, (3) the effects of eye movements on perception, and (4) visual field assessment. The reviewed studies support the idea that eye tracking is a valuable technique for the study of basic perceptual processes. We discuss methodological characteristics within each of the proposed classification area, with the objective of informing future task design.

A Dietary Strategy for Optimizing the Visual Range of Athletes

Visual range is quantified by assessing how far one can see clearly (an ability crucial to many athletes). This ability tends to vary significantly across individuals despite similar personal characteristics. We hypothesize that the primary driver of these differences is the individual response to scattered short-wave light in the environment moderated by the dietarily derived retinal pigments lutein and zeaxanthin.

A clínica da psicofísica

Apresentamos a Psicofísica como uma ciência aplicada nas investigações e nas abordagens e diagnósticos clínicos. Inicialmente, introduzimos algo dos aspectos epistemológicos e teóricos da área, passamos para as abordagens que a Psicofísica pode apresentar na aplicabilidade clínica e, por fim, discutimos os avanços recentes da aplicação clínica, apresentamos as experiências de nosso laboratório de pesquisa clínica em psicofísica, finalizando com as perspectivas de ampliação do uso da psicofísica para investigações clínicas de funções perceptuais mais complexas.

Contrast sensitivity in seasonal and nonseasonal depression

BACKGROUND

Psychophysics has been used for the early diagnosis of many diseases that affect the visual pathway including those not usually considered vision-related (e.g., Parkinson's disease). Little has been done, however, to investigate visual functioning in psychological disorders known to be effectively treated by phototherapy. We measured the static and dynamic spatial contrast detection thresholds of seasonally depressed (SAD), nonseasonally depressed (Depressed) and nondepressed (Control) individuals.

METHODS

Two psychophysical experiments which measured luminance contrast detection thresholds were conducted. Experiment 1 presented static, vertically oriented Gabors with center spatial frequencies ranging from 0.3 to 12.0 cpd (cycles per degree). Experiment 2 presented 0.5, 1.5 and 4.0 cpd Gabors whose phases were sinusoidally reversed at 2.0, 4.0, 8.0, 16.0, and 32.0 c/s (Hz).

RESULTS

SAD showed significantly greater contrast sensitivities than Controls for static spatial frequencies equal to or greater than 6.0 cpd. Depressed showed significantly greater contrast sensitivities at 6.0 cpd and 12.0 cpd. With phase modulation, the SAD group showed significantly enhanced contrast sensitivity with 4.0 cpd-2.0 Hz Gabors. All other results at lower spatial-higher temporal frequencies were not significant.

LIMITATIONS

Most of the subjects were drawn from the student population instead of the community or clinics, even though they met the criteria for clinical depression. Antidepressant use was not controlled for among the subjects.

CONCLUSIONS

These findings suggest that clinical depression can enhance contrast sensitivity when stimuli elicit strong parvocellular responses. These enhancements implicate differences in retinal functionality. Mechanisms that link neuromodulatory activity to retinal signal processing are proposed.