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C Bonnet

Publications and source records attributed to C Bonnet.

At least 109 records · Page 6Linked to original sources
PubMed1989

Visual adaptation to a spatial contrast enhances visual evoked potentials.

The effects of adaptation to the visual contrast of a counterphase grating were studied with visual evoked potentials (VEPs). The spatial frequency of the grating was 4 cpd, and its temporal frequency was 4 or 12 Hz. Steady-state VEPs were analyzed through an FFT (fast Fourier transform) algorithm. In the first experiment, contrast thresholds rose strongly just after the end of adaptation and declined regularly over time. The VEPs recorded in the medio-occipital lead showed an initial decrease in amplitude after adaptation, followed by an enhancement well above the preadaptation level and then a return to that level. The paradoxical enhancement of the VEP was found at both high and low contrast in both the medio-occipital lead and the right temporal lead of a right-handed subject. The left temporal leads showed a VEP enhancement at high contrast and a decline at a low value.

Attention↗
PubMed1986

Hemispheric asymmetries in the visual evoked potentials to temporal frequency: preliminary evidence.

Steady-state evoked potentials were recorded in eight adult subjects from occipital and temporal leads of both hemispheres to investigate the effect of temporal frequency on the hemispheric specialization for basic visual information. A 3 cycles deg-1 grating was phase-reversed at different temporal frequencies (from 4 to 18 Hz), and the frequency spectrum of evoked potentials was computed by means of a fast Fourier transform program. Significant results were obtained for the component at twice the temporal frequency of stimulation. Occipital evoked potentials did not show hemispheric asymmetry, whereas temporal evoked potentials showed an interaction between hemisphere and temporal frequency: right and left hemispheres were respectively prominent for low (4 and 6 Hz) and for high (8-18 Hz) temporal frequencies. The results are discussed in the context of current research on hemispheric specialization for basic spatiotemporal parameters of visual information processing.

Adult↗
PubMed1984

Discrimination of velocities and mechanisms of motion perception.

In a first experiment, velocity discrimination thresholds were measured in twenty-one experimental conditions by presentation of successive pairs of standard/comparison motions of a single spot target. Exposure times between 300 to 900 ms did not affect velocity discrimination. However, very slow velocity increased discrimination thresholds. Velocity discrimination is improved by the presence of stationary references and decreased by eccentricity. At slow velocities, in the absence of a motion phase, a discrete mode of presentation of the translation leads to higher discrimination thresholds than those observed with the continuous and stop-go-stop modes of the same translation. In a second experiment, it was shown that for shorter exposure time (100 ms), discrimination thresholds are much higher for the discrete mode. It is concluded that at long exposure time, velocity discrimination thresholds are essentially independent of the presence of a motion phase.

Differential Threshold↗
PubMed1984

Two systems in the detection of visual motion.

Several groups of authors have suggested separate mechanisms for the detection of motion and for the detection of pattern characteristics of the same stimuli [Kulikowski, J. J. and Tolhurst, D. J. (1973) J. Physiol., Lond. 232, 149-163; and King-Smith, P. E. (1978) In Armington, J. C., Krauskopf, J. and Wooten, B. R. (Eds) Visual Psychophysics and Physiology. Academic Press, New York]. Their stimuli were generally in the frequency domain. Bonnet [(1975) Psychologia 18, 35-50; (1977) Perception 6, 491-500; and (1982) In Wertheim, A. H., Wagenaar, W. A. and Leibowitz, H. W. (Eds) Tutorials in Motion Perception. Plenum, London] has developed a conceptual model of motion detection in the space-time domain. Two systems are assumed: a movement-analysing system (MAS) which processes the motion phase of any translation and a displacement-analysing system (DAS) which processes the successive stationary components of the stimulus. These proposed mechanisms are studied in experiments which use three different modes of translation of a single spot: continuous, discrete and stop-go-stop. The first mode should preferentially trigger the MAS, the second mode the DAS, while the stop-go-stop mode is a test mode. The results show that for short exposure times (less than or equal to 180 ms) the velocity thresholds for the continuous mode are greater than for the other two modes. For these durations, thresholds of the continuous mode are not lowered by the availability of stationary reference points. The effects of luminance on the results with the three modes support the basic model.

Humans↗
PubMed1978

[Purulent pleurisy caused by anaerobic bacteria. Apropos of 2 observations].

Purulent pleural effusions due to anaerobic organisms secondary to infections of the pulmonary parenchyma are complications which often occur following the inhalation of organisms from the buccal cavity. The most commonly found organisms belong to the endogenous anaerobic flora of Veillon. Rapid encystment of the pleural collection is suggestive of this diagnosis. Treatment consists of drainage of the cavity associated with specific antibiotics.

Adult↗
PubMed1977

Visual motion detection models: features and frequency filters.

Two kinds of models have been proposed for taking into account the sensory processes at work in the detection of visual motion: the feature model and the frequency-filter model. The problem of the complementarity of these models is raised. On the basis of empirical data, it is proposed that they are consistent.

Differential Threshold↗