Biomedical subjects

Sophie M Wuerger

Publications and source records attributed to Sophie M Wuerger.

4 recordsLinked to original sources

PubMed2005

Low-level integration of auditory and visual motion signals requires spatial co-localisation.

It is well known that the detection thresholds for stationary auditory and visual signals are lower if the signals are presented bimodally rather than unimodally, provided the signals coincide in time and space. Recent work on auditory-visual motion detection suggests that the facilitation seen for stationary signals is not seen for motion signals. We investigate the conditions under which motion perception also benefits from the integration of auditory and visual signals. We show that the integration of cross-modal local motion signals that are matched in position and speed is consistent with thresholds predicted by a neural summation model. If the signals are presented in different hemi-fields, move in different directions, or both, then behavioural thresholds are predicted by a probability-summation model. We conclude that cross-modal signals have to be co-localised and co-incident for effective motion integration. We also argue that facilitation is only seen if the signals contain all localisation cues that would be produced by physical objects.

Acoustic Stimulation↗

PubMed2005

The cone inputs to the unique-hue mechanisms.

Our aim was to characterise the chromatic mechanisms that yield the four unique hues: red, green, yellow and blue. We measured the null planes for all four unique hues and report the following two main results. (1) We confirm that three chromatic mechanisms are required to account for the four unique hues. These three chromatic mechanisms do not coincide with the chromatic tuning found in parvocellular LGN neurones, i.e., neurones tuned to L-M and S-(L+M); these subcortical chromatic mechanisms are hence not the neural substrate of the perceptual unique hues and further higher-order colour mechanisms need to be postulated. Our results are consistent with the idea that the two higher-order colour mechanisms that yield unique red and unique green respectively combine the incremental and decremental responses of the subcortical chromatic mechanisms with different weights. In contrast, unique yellow and unique blue can be explained by postulating a single higher-order chromatic mechanism that combines the incremental and decremental subcortical chromatic responses with similar weights. (2) The variability between observers is small when expressed in terms of perceptual errors, which is consistent with the hypothesis that the colour vision system in adult humans is able to recalibrate itself based on prior visual experience.

Adult↗

PubMed2005

The perception of motion in chromatic stimuli.

The issue of whether there is a motion mechanism sensitive to purely chromatic stimuli has been pertinent for the past 30 or more years. The aim of this review is to examine why such different conclusions have been drawn in the literature and to reach some reconciliation. The review critically examines the behavioral evidence and concludes that there is a purely chromatic motion mechanism but that it is limited to the fovea. Examination of motion performance for chromatic and luminance stimuli provides convincing evidence that there are at least two different mechanisms for the two kinds of stimuli. The authors further argue that the chromatic mechanism may be at a particular disadvantage when the integration of multiple local motion signals is required. Finally, the authors present a descriptive model that may go some way toward explaining the reasons for the differences in collected data outlined in this article.

Color Perception↗

PubMedDate not supplied

The chromatic input to global motion perception.

For over 30 years there has been a controversy over whether color-defined motion can be perceived by the human visual system. Some results suggest that there is no chromatic motion mechanism at all, whereas others do find evidence for a purely chromatic motion mechanism. Here we examine the chromatic input to global motion processing for a range of color directions in the photopic luminance range. We measure contrast thresholds for global motion identification and simple detection using sparse random-dot kinematograms. The results show a discrepancy between the two chromatic axes: whereas it is possible for observers to perform the global motion task for stimuli modulated along the red-green axis, we could not assess the contrast threshold required for stimuli modulated along the yellowish-violet axis. The contrast required for detection for both axes, however, are well below the contrasts required for global motion identification. We conclude that there is a significant red-green input to global motion processing providing further evidence for the involvement of the parvocellular pathway. The lack of S-cone input to global motion processing suggests that the koniocellular pathway mediates the detection but not the processing of complex motion for our parameter range.

Artifacts↗