Biomedical subjects

Jocelyn Faubert

Publications and source records attributed to Jocelyn Faubert.

25 records · Page 2Linked to original sources

PubMed2002

Aging effects on intra- and inter-attribute spatial frequency information for luminance, color, and working memory.

Visual working memory (VWM) for spatial frequency information was assessed in both young and older observers. In the first experiment we assessed the effect of a memory mask on a VWM task. We found no effect of mask on retention for either the young or older groups. This argues against the 'inhibition' hypothesis of aging in regards to visual processing, which suggests that the elderly should have difficulty to inhibit irrelevant information. We conclude that the suggestion of an inefficient inhibition process in aging derived from evidence obtained for higher-level WM tasks cannot be generalized to the discrimination of basic patterns in VWM. The second experiment focused on processing resources within VWM by assessing VWM for intra-attribute (color or luminance), and inter-attribute (color and luminance)-defined spatial frequency information. Results show that retention of spatial frequency information in VWM is robust for both the younger and older group regardless of the defining attribute. Thresholds were significantly higher in the inter-attribute condition, indicating increased processing demands for this task and suggesting that these attributes are initially processed in parallel. Older observers showed higher discrimination thresholds than young observers for all conditions indicating a deficit in perceptual abilities rather than in VWM for basic stimuli. The difference in thresholds for the older group was highest in the inter-attribute condition suggesting that older observers show more deficits on visual tasks with increased processing demands.

Aged↗

PubMed2002

The perceived speed of drifting chromatic gratings is mechanism-dependent.

The perceived speed of chromatic motion was investigated for gratings that stimulate each chromatic mechanism [L-M and S-(L+M)] in isolation and for gratings that stimulate both chromatic systems. The observers' task consisted of adjusting the speed of a drifting achromatic grating to match the perceived speed of an isoluminant chromatic grating, drifting at 8 deg/s (temporal frequency of 4 Hz). Every observer reported a substantial decrease in perceived speed for chromatic gratings modulated along the S-(L+M) (blue-yellow) cardinal axis compared to other directions in color space. One observer even reported motion standstill for gratings modulated along this axis. Further testing demonstrates that the perceived speed of an isoluminant chromatic grating depends solely on the extent to which it stimulates the L-M (red-green) mechanism. Thus, under the conditions that were tested, the S-(L+M) postreceptoral mechanism does not appear to contribute significantly to determining the perceived speed of chromatic motion.

Color Perception↗

PubMed2002

Central and peripheral interactions in the perception of optic flow.

The purpose of this work was to evaluate the effects of central and peripheral stimulation on the perception of optic flow over large spatial extents. Coherence thresholds were measured for RDKs simulating observer translation and radial motion. Experiments 1 and 3a measured sensitivity to a range of speeds for a circular central region, for several annular regions of increasing eccentricity, and for a full-field stimulus (80 degrees diameter). Results suggest that the spatial extent over which signals are integrated may vary in order to maximize the information available for perceptual representations. Experiments 2 and 3b evaluated central and peripheral interactions in a direction discrimination task, by comparing the effects of different signal strengths and directions in one of the two regions. The presence of noise dots (0% coherence) in either center or periphery led to a performance decrease from baseline measures. A similar decrease was observed when dots in the two regions moved in opposite directions. When dots in both regions moved in the same direction, a stronger peripheral signal led to facilitation of direction discrimination, whereas a stronger central signal did not. These findings suggest that central and peripheral inputs are not separable in the integration of optic flow, that they contribute equally to the percept under normal conditions (equal signal strength), and that peripheral stimulation seems important under ecologically relevant conditions such as poor visibility.

Discrimination, Psychological↗

PubMed2002

Visual perception and aging.

A series of studies performed in our laboratory on aging and its effect on perceptual processing and working memory capacity for visual stimuli are reviewed. Specifically, studies on luminance, colour, motion, texture, and symmetry processing are reported. Furthermore, experiments on the capacity to retain size and spatial frequency information are also discussed. The general conclusion is that there are a number of perceptual abilities that diminish with age. However, the extent of these deficits will depend on the complexity of the neural circuitry involved for processing a given task. This is also true for visual working memory where no evidence of loss due to aging is demonstrated for processing low-level visual information, when individual differences in sensory input are compensated for. It is concluded that perceptual processing deficits due to aging (like working memory) will become evident when the computational load reaches a certain level of complexity (larger or more complex network) even if the tasks remain cognitively simple.

Aged↗

PubMed2002

Aging and bilateral symmetry detection.

The salience of bilateral symmetry varies as a function of the orientation of the symmetry axis. Vertical symmetry is most salient, followed by horizontal and then oblique orientations. We tested symmetry detection in different age groups to determine whether performance of this intermediate-level visual task is affected by normal, nonpathological aging. We tested forty participants and analyzed the results with respect to age group and symmetry orientation (vertical, horizontal, and 45 degree oblique). There was a vertical symmetry detection advantage for all participants, where sensitivity was highest for vertical symmetry, followed by horizontal symmetry, and then the oblique symmetry. Sensitivity to symmetry did not differ for the two younger age groups (aged 19-39 and 40-60), but declined significantly for the group aged 61-70, and declined again for the oldest group aged 71-80. This age-related difference in sensitivity to symmetry was not reflected in a measure of bias, where there were no differences as a function of age.

Aging↗

PubMedDate not supplied

Visual evoked potentials and reaction time measurements to motion-reversal luminance- and texture-defined stimuli.

PURPOSE: Previous studies have suggested that compared to first-order (FO) motion stimuli, second-order (SO) motion stimuli required more cortical time to be processed. The purpose of this study was: 1- to verify this claim with Visual Evoked Potential (VEP) and eye-hand Reaction Time (RT) measurements and 2- examine if the VEP and RT responses are similarly modulated by the same trigger features of the stimuli. METHODS: The VEPs and eye-hand RT for motion-reversal luminance- (first-order) and texture-defined (second-order) stimuli were recorded from ten normal human subjects. VEPs and RTs were measured for each motion class at eight different modulation depths (from 3 to 100%). RESULTS: Our results reveal that for stimuli of low contrast levels, the SO-FO timing differences are approximately 100 ms (RT) or 20 ms (VEP), while for contrasts >or= 15-20% (VEP) or >or= 50% (RT), the SO-FO difference is no longer significant (p < 0.007), suggesting either that the brain can no longer distinguish SO from FO stimuli or that in spite of the added complexity of SO stimuli the brain takes equal time to process both. CONCLUSION: Interestingly, the above contrast discrepancy in SO-FO resolution threshold suggests that, compared to the VEP, the more psychophysical RT measurement can process and thus distinguish a larger spectrum of motion stimuli, thus further confirming the latter measure of the retinocortical processing time as a valid alternative to the VEP.

Adolescent↗

PubMedDate not supplied

The moving dynamic random dot stereosize test: validity and repeatability.

PURPOSE: We have developed a new test suitable for measuring stereopsis in young children and individuals with communication difficulties. It consists of a drifting, computer-generated red and green, dynamic random dot, disparate shape. The motion direction is indicated by the subject (subjective response) or by a naive observer judging the eye movements of the subject (objective response). Disparity is maintained at 616 sec arc and the dependent variable is the angular subtense of the target, which varies from 11 degrees to 11 ft. In this study, precision (ie, measuring repeatability and objective-subjective agreement) and validity were assessed. SUBJECTS AND METHODS: Sixteen subjects with normal vision participated in the repeatability study and 10 in the validity studies. A two-up/one-down, 2 alternative forced choice staircase procedure was used to measure objective and subjective threshold on two occasions with a 1-week separation. Sensitivity for detecting anisometropia was estimated with simulated anisometropia (0 to 3 D) and by comparison with the Randot test. Sensitivity for detecting amblyopia or strabismus was tested in 10 subjects. RESULTS: Subjective repeatability was 0.31 log units (2 levels of the test) and objective repeatability was 0.49 log units (3.2 levels of the test). The test was able to detect 2.0 D of simulated anisometropia in 8 of 10 cases (above the 95% confidence interval). None of the amblyopic subjects demonstrated stereopsis. CONCLUSION: This test of dynamic global stereopsis has potential as a clinical or screening tool for anisometropia, amblyopia, and strabismus.

Adult↗