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C Bonnet

Publications and source records attributed to C Bonnet.

At least 109 records · Page 6Linked to original sources
PubMed1990

Apparent brightness enhancement in the Kanizsa square with and without illusory contour formation.

The perceived strength of darkness enhancement in the centre of surfaces surrounded or not surrounded by illusory contours was investigated as a function of proximity of the constituent elements of the display and their angular size. Magnitude estimation was used to measure the perception of the darkness phenomenon in white-on-grey stimuli. Darkness enhancement was perceived in both types of the stimuli used, but more strongly in the presence of illusory contours. In both cases, perceived darkness enhancement increased with increasing proximity of the constituent parts of the display and with their angular size. These results suggest that the occurrence of darkness (or brightness) enhancement phenomena in the centre of the displays is not directly related to illusory contour formation.

Adult↗
PubMed1990

[The image of intravertebral somatic gaseous dissection. Report of 9 cases one of which has a triple localization and review of the literature].

We report a series of 9 cases of vertebral somatic gaseous dissection studied between 1978 and 1989. We find most of the characteristics established from the literature data: advanced age, possible medullar compression contrary to the vertebral compression by common osteoporosis, predilection for the dorso-lumbar junction, frequency of the osteoporosis, possibility of metabolic disorders, of occurrence after radiotherapy. The context of the occurrence and the paraclinical examinations of the whole have enabled us to eliminate, in this series, a malignant pathology. However, when there exists a doubt on a malignant origin, it is preferable to carry out a vertebral biopsy with a trocar. In fact, the image may not be pathognomonic of a benign vertebral osteoporosis. Finally, we give the first description of a triple localization of vertebral gaseous dissection.

Aged↗
PubMed1990

[Can oximetry contribute to the detection of apnea? The use of a mathematical analysis of the oximetry signal].

The aim of this study was to test the efficacy of nocturnal oximetry as a means of continuous recording of SaO2 in the identification of apnoeic events in the recognition of non-apnoeic desaturation. The oscillations of SaO2 in relation to successive periods of apnoea during the course of the sleep apnoea syndrome (SAS) or with apnoeic episodes in patients with chronic airflow obstruction (BPCO) or restricted disease, were identified using a new delta index quantifying the variations of SaO2 during the night. 26 successive patients in whom there was an indication for nocturnal oximetry were included in a prospective study comparing nocturnal oximetry and polysomnography during 34 nights. In the apnoeic patients we found a strong correlation (r = .85. p. less than .01) between the apnoeic period and the delta index. In BPCO the number of apnoea was correlated with the delta index (r = .96. p. less than .01). A minimal threshold of the delta index fixed at 1.5 was satisfactory for detecting apnoea if the initial SaO2 was less than 93%. The value of the adequate for affected detection ought to be fixed at .8 (95% sensitivity) when the initial SaO2 was greater than 93%. A detection of apnoeic events thus seems possible by this method.

Apnea↗
PubMed1989

Influence of spatial frequency and handedness on hemispheric asymmetry in visually steady-state evoked potentials.

Recent suggestions on the involvement of the spatial frequency of visual stimuli in the hemispheric lateralization were investigated by recording steady-state evoked potentials in two groups of subjects: five right-handers and five left-handers. Sinusoidal gratings at spatial frequency of 0.5, 1, 3, 4, 6, 8, 10, 12 or 16 cpd were phase reversed at 4 Hz or 12 Hz. Evoked potentials recorded from temporal leads over each hemisphere were submitted to a FFT analysis. Results concern the amplitude of the fundamental component. In right-handers, the temporal frequency was the deciding factor of the lateralization: the evoked activities were greatest in the RH at 4 Hz and in the LH at 12 Hz. This effect was obvious for the range of spatial frequencies from 3-12 cpd. Results, discussed in terms of global/local information, suggested the existence of two transient and sustained systems. In left-handers, both the spatial and temporal parameters were relevant to the lateralization. A spatio-temporal interaction was observed which was reversed at 6 cpd.

Adult↗
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↗