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Biomedical subjects

T Caelli

Publications and source records attributed to T Caelli.

At least 55 records · Page 3Linked to original sources
PubMed1982

Contrast sensitivity in diabetics with retinopathy and cataract.

Contrast sensitivity responses were determined in diabetic subjects with retinopathy, macular disease and cataract. The test proved reliable in discriminating between different degrees of cataract and between diabetics with no retinopathy, mild background retinopathy and early maculopathy. Background retinopathy was shown to produce a loss of contrast sensitivity particularly at the low and medium frequencies. These thresholds increased with macular involvement. Mild cataract was correlated with loss at the low and medium spatial frequencies, whilst moderate cataract suppressed sensitivity to all frequencies. Results are compared to colour discrimination in each patient.

Adolescent↗
PubMed1982

Visual sensitivity to two-dimensional spatial phase.

We investigate some limits to phase processing in the human visual system with two-dimensional textured images. Results indicate that, although phase sensitivity increases with contrast and energy components of the image, observers cannot discriminate between images and their 45 degrees phase-quantized versions under brief exposure and lower- (less than or equal to 30%) contrast conditions. These results seem to be frequency independent although modulated by different energy levels at each two-dimensional frequency band. Finally, we have analyzed some past texture-discrimination results that occur under identical amplitude-spectra conditions. Here also phase-quantization differences seem to constitute an adequate explanation of discrimination performance.

Humans↗
PubMed1982

Modelling perceptual distortion: amplitude and phase transmission in the human visual system.

In this paper we consider the complementary properties of image amplitude and phase components and their role in normal and amblyopic vision. Specific two-dimensional filtered images are included to demonstrate the possible perceptual distortions due to both amplitude and phase disturbances. Finally, the relationships between amplitude and phase filters are discussed with reference to the types of receptive field distributions expected to underly the normal and abnormal cases.

Amblyopia↗
PubMed1981

On the spatio-temporal determinants of some motion effects.

In a series of recent experiments we have examined the effects of varying the spatio-temporal determinants of some motion configurations on the geometric properties of the perceived motions. For both apparent motion and the kinetic depth effect (being two representative motion sources) specific spatio-temporal frequency and phase limits have been determined with respect to the various (geometrically defined) percepts Finally, a network is proposed which enables predictions about perceived motion loci (and other geometric features), based on the equating of the observed spatio-temporal limits with the bandwidth for a filtering mechanism.

Depth Perception↗
PubMed1981

Intensity, spatial frequency, and temporal frequency determinants of apparent motion: Korte revisited.

The authors have earlier found support for the notion that apparent motion (AM) is mediated by a low-pass temporal-frequency filter operating over the spatial domain of the AM sources. Experiments have been carried out to test how this response is changed, or unchanged, through varying the source intensities or contrasts. The results indicate no intensity or contrast effects on the spatiotemporal limits for AM. These results are related to the early formulations of Korte and indicate that there is no amplitude-modulation or contrast-sensitivity function for AM--as there is for threshold movement detection. The filter mechanism seems to be largely restricted to the spatiotemporal domain.

Discrimination Learning↗
PubMed1979

On the perception of some geometric properties of rotating three dimensional objects.

Various observations and conjectures have been made about how we perceive three dimensional objects under monocular viewing conditions; in particular, when such objects are rotating. In this paper these proposals are reviewed and reinterpreted in the light of geometric properties of objects and their projections. Some results are also presented which support the conclusion that the visual system, in reconstructing the object from its projections, requires a fixed time to establish the objects curvature and torsion parameters. In the perceptual reconstruction process these parameters assume positive or negative values, and this equivocation is related to a form of the adjacency principle involving central projections and "perceptual geodesics".

Form Perception↗
PubMed1979

Frequency, phase, and colour coding in apparent motion.

We present some results which indicate that the known spatiotemporal limits for apparent motion are consistent with the motion being sinusoidal or a result of filtering. Given this we investigated how two such motions interact as a function of their relative temporal phase differences. This was accomplished by inducing two independent motions from complementary coloured event pairs. Results indicated critical phase limits for perceiving the two motions (red and green) which were consistent with the frequency specificity of the effect. The results are discussed within the framework of a filtering process for the perception of apparent motion.

Color Perception↗
PubMed1979

On the limits of Fourier decompostitions in visual texture perception.

Recent discoveries of nonlinear perceptual analyzers in effortless texture discrimination cast serious doubt on the usefulness of Fourier image decompositions to describe suprathreshold visual-texture perception. We now explain the meaning of these results.

Discrimination, Psychological↗
PubMed1979

Frequency, phase, and colour coding in apparent motion: 2.

In an earlier paper, Caelli and Finlay demonstrated that the perception of apparent motion was contingent on critical phase relationships between inducing sources, and their spatio-temporal frequency ranges. In their original stimulus red-green centre-surround sources were used and phase-specific inhibition was found at 60 degrees--90 degreee phase angle differences between the complementarily coloured elements. In this experiment we show that, when centre-surround sources are replaced by vertically-horizontally displaced complementary (or identically coloured) sources, symmetrical phase inhibition effects occur with both motions.

Color Perception↗
PubMed1979

Psychophysical evidence for global feature processing in visual texture discrimination.

By defining texture as a global feature attained by integration over the image domain, we show that texture discrimination can be predicted for a special class of visual textures (composed of paired dots) as a function of such global features. We derive a psychophysical law based on these global features and show that differences in the variance of orientation, but not of dipole length, result in texture discrimination.

Form Perception↗