Renata Maria Toscano Barreto Lyra Nogueira

Comparison of angular frequency contrast sensitivity in young and older adults

The aim of the present study was to measure contrast sensitivity curves for angular frequencies in the range between 2 and 96 cycles/360 masculine in older human adult volunteers and to compare these measurements with the more usual contrast sensitivity functions for sine-wave gratings. All subjects were free of identifiable ocular disease and had normal acuity. We measured the contrast thresholds for young adults (N=6; age range, 20-26 years) and older adults (N=6; age range, 60-67 years) using the psychophysical forced-choice method. In this paradigm the volunteers had to choose the stimulus containing a test frequency at low contrast (e.g., either a sine-wave grating or an angular frequency stimulus), or another neutral stimulus at mean luminance (without any contrast). Older adults presented a loss in contrast sensitivity at high and medium angular frequencies compared to the young adults (i.e., from 8 to 96 cycles/360 degrees). Contrary to expectation, contrast sensitivity at low angular frequencies, i.e., 2 and 4 cycles/360 degrees, was better for the older group than for the younger group. On the other hand, contrast sensitivity for sine-wave gratings at 3 and 4 cpd was higher for young adults as expected. These results suggest age-related changes in the contrast sensitivity function for angular frequencies.

Processamento visual da forma em idosos: curvas de limiar de contraste para freqüências angulares e senoidais

The aim of this work was to measure contrast sensitivity curves for angular and spatial frequencies in the aged. We measured the contrast thresholds from young adults (20-26 years-old) and aged (60-67 years-old). All the participants had good visual acuity and were free from significant ocular pathology. The angular and spatial frequencies measured with a forced-choice psychophysic method were 2, 4, 8, 16, 24, 32, 48, 64 and 96 cycle/360o and 0.5, 1, 2, 3, 4, 6 and 9 cpd, respectively. The results showed a loss in contrast sensitivity for the aged at high and medium angular and spatial frequencies compared to the younger group. We still found that the contrast sensitivity of the aged group at low angular frequency is better than the younger group. These results are consistent with age-related changes in contrast sensitivity function.

Processamento visual da forma: evidências para canais múltiplos de freqüências angulares em humanos

O objetivo deste trabalho foi caracterizar e comparar curvas de resposta do sistema visual humano para filtros de frequencias a ngulares de 1e 4 ciclos/360o em coordenadas polares. Mensuramos 15 curvas para cada filtro com o paradigma de somacao de resposta de suprali miar ecom a participacao de 5 voluntarios adultos. Os resultados demonstraram somacoes maximas de limiar de contraste na frequencia d e teste dosfiltros angulares (1 e 4 ciclos/360

Radial frequency stimuli and sine-wave gratings seem to be processed by distinct contrast brain mechanisms

An assumption commonly made in the study of visual perception is that the lower the contrast threshold for a given stimulus, the more sensitive and selective will be the mechanism that processes it. On the basis of this consideration, we investigated contrast thresholds for two classes of stimuli: sine-wave gratings and radial frequency stimuli (i.e., j0 targets or stimuli modulated by spherical Bessel functions). Employing a suprathreshold summation method, we measured the selectivity of spatial and radial frequency filters using either sine-wave gratings or j0 target contrast profiles at either 1 or 4 cycles per degree of visual angle (cpd), as the test frequencies. Thus, in a forced-choice trial, observers chose between a background spatial (or radial) frequency alone and the given background stimulus plus the test frequency (1 or 4 cpd sine-wave grating or radial frequency). Contrary to our expectations, the results showed elevated thresholds (i.e., inhibition) for sine-wave gratings and decreased thresholds (i.e., summation) for radial frequencies when background and test frequencies were identical. This was true for both 1- and 4-cpd test frequencies. This finding suggests that sine-wave gratings and radial frequency stimuli are processed by different quasi-linear systems, one working at low luminance and contrast level (sine-wave gratings) and the other at high luminance and contrast levels (radial frequency stimuli). We think that this interpretation is consistent with distinct foveal only and foveal-parafoveal mechanisms involving striate and/or other higher visual areas (i.e., V2 and V4).

Processamento visual da forma em humanos: curvas de limiar de contraste para padrões circularmente simétricos

The aim of this work was to measure contrast sensitivity curves to concentrically symmetric patterns in a system of polar coordinates. We measured the contrast thresholds to sine wave gratings, radial frequencies and coupled radial/angular frequencies. Six young adults with corrected-to-normal visual acuity participated in the experiments. The frequencies measured with a forced-choice psychophysical method were 0.2, 0.3, 0.5, 0.8, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 and 9.0 cpd. Results showed that coupled radial/angular frequencies caused an increase in the sensitivity of at least 1.6 times in relation to radial contrast sensitivity function. These results were in agreement with the model of multiple channels processing of spatial frequencies of stimuli defined in terms of polar coordinates.

Colour discrimination thresholds in type 1 Bipolar Disorder: a pilot study

Although some studies have reported perceptual changes in psychosis, no definitive conclusions have been drawn about visual disturbances that are related to bipolar disorder (BPD). The purpose of the present study was to evaluate colour vision in BPD patients. Data were recorded from 24 participants: healthy control group (n = 12) and type 1 BPD group (n = 12). The participants were 20–45 years old and they were free from neurological disorders and identifiable ocular disease and had normal or corrected-to-normal visual acuity. Colour discrimination was evaluated using the Lanthony D-15d, Trivector and Ellipse tests, using a psychophysical forced-choice method. The relationship of visual measures to mood state and cognitive function was also investigated. The results showed that BPD patients had higher colour discrimination thresholds in the D15d (p < 0.001), Trivector (p < 0.001) and Ellipse (p < 0.01) tests compared with healthy controls. Linear regression analysis showed that mood state was related to colour discrimination. BPD individuals were not impaired in cognitive tasks. The present study provided new evidence of potential links between type 1 BPD and visual processing impairments. This research suggests a new direction for studies and the need for research in this field of study.

Construção e evidências psicométricas de uma escala de avaliação da percepção visual

Este estudo teve como objetivo construir e conhecer os parâmetros psicometricos de um instrumento para analise da percepcao visual de adultos. Para a construcao da escala participaram 295 adultos saudaveis, sem deficits cognitivos ou perceptivo-visuais. Nesta etapa foi formulada uma escala tetrafatorial constituida por 20 itens que avaliam quatro dimensoes referentes a percepcao visual: constância da forma, figura-fundo, posicao e relacao espacial. Para obter evidencias de validade foi utilizada uma amostra de 183 voluntarios com boa saude fisica e mental e acuidade visual normal ou corrigida. Os dados obtidos relatam a existencia de concordância interjuizes, adequacao semântica e significância no teste-reteste do instrumento. Os coeficientes de fidedignidade variaram de 0,84 a 0,93. Os quatro fatores esperados foram encontrados, cada um contendo 5 itens, e juntos explicaram 57,52% da variância do constructo. O instrumento apresentou parâmetros psicometricos adequados, o que pode justificar sua utilidade em pesquisas basicas e na pratica clinica.

Percepção visual de contraste em humanos: evidência psicofísica para canais de freqüência angular alta

The aim of this study was to measure narrow-band frequency response curves for four angular frequency filters. The test frequencies were 32, 48, 64 and 96 cycles/360o. Six humans observers with normal or corrected visual acuity measured nine curves for each filter, with a supra-threshold response summation psychophysical method allied with a forced-choice method. The results showed maximum summation effects at test frequency for filter frequencies 32, 48, 64 and 96 cycles/360o, as well as a strong inhibition for neighboring frequencies. These results are consistent with the existence of narrow-band angular frequency filters in the human visual system either through summation or the inhibition of specific high angular frequency ranges.

Matlab and eye-tracking: applications in psychophysics and basic psychological processes

This article aims to demonstrate the utilities of Matlab (MATrix LABoratory) and eye-tracker for research in psychophysics and basic processes. We fi rst introduce its origin, functioning, and advantages over other programs, and then we review different applications of Matlab in psychophysical tests involving eye-trackers. As an example, we present the development of a psychophysical test involving eye-tracker and Matlab, showing its ability to communicate and interact with other devices and programming languages. Finally, we emphasize the advantages and diffi culties of working with Matlab.

O uso de pinturas de Dalí como ferramenta para avaliação das alterações na percepção de forma e tamanho em pacientes esquizofrênicos

Estudos envolvendo portadores de esquizofrenia tem mostrado alteracoes severas da percepcao e cognicao. A maioria dos diagnosticos, entretanto, e baseada na avaliacao de processos cognitivos. Nossos estudos investigaram a percepcao alterada de forma e tamanho em pacientes com esquizofrenia e com depressao maior utilizando 24 pinturas de Salvador Dali. Conduzimos dois estudos comparando grupos experimental e controle e observamos, em ambos os casos, que os portadores de esquizofrenia perceberam figuras 1,5 e 3,0 vezes maior do que os respectivos grupos controle. Em outro estudo com pacientes com depressao maior nao foram observadas alteracoes na percepcao de tamanho comparado ao grupo controle. Concluimos que este efeito de percepcao de forma e tamanho alterados pode servir como marcador no diagnostico precoce da presenca de sintomas positivos na esquizofrenia. Sugerimos que estas pinturas de Salvador Dali sejam utilizadas como ferramenta para avaliar alteracoes na percepcao de formas e tamanhos em pacientes portadores de esquizofrenia e, assim, prevenir o agravamento dos sintomas cognitivos.