Biomedical subjects

W Joung

Publications and source records attributed to W Joung.

3 recordsLinked to original sources

PubMed2000

Tilt aftereffects generated by bilaterally symmetrical patterns.

Tilt aftereffects were generated by bilaterally symmetrical dot patterns. Both expansion and contraction effects, similar in size and magnitude to effects usually reported with luminance contours, were observed after adaptation to symmetrical patterns tilted 15 deg or 75 deg respectively from a vertically oriented test. Large effects were found when both adapting and test stimuli were symmetrical patterns while smaller effects were found when the adapting stimulus was symmetrical and test stimulus was a grating. A third experiment, which manipulated the number of dots near the axis line, confirmed the above findings; expansion and contraction effects were observed again. The results of these experiments suggest that the neural mechanism underlying the perception of luminance contours may be linked to the mechanism for the detection of symmetry.

Adaptation, Ocular↗

PubMed1998

Evidence that both area V1 and extrastriate visual cortex contribute to symmetry perception.

Bilateral symmetry is common in nature and most animals seem able to perceive it. Many species use judgements of symmetry in various behaviours, including mate selection [1-3]. Originally, however, symmetry perception may have developed as a tool for generating object-centered, rather than viewer-centered, descriptions of objects, facilitating recognition irrespective of position or orientation [4]. There is evidence that the visual system treats the orientation of axes-of-symmetry in the same way it treats in orientation of luminance-defined contours [5], suggesting that axes-of-symmetry act as 'processing tokens' [6]. We have investigated the characteristics of neural mechanisms giving rise to the perceived orientation of axes-of-symmetry. We induced tilt aftereffects with symmetrical dot patterns, eliciting perceived angle expansion and contraction effects like those usually observed with luminance-defined contours [7,8]. Induction of aftereffects during binocular rivalry resulted in a reduction of the magnitude of these effects, consistent with the aftereffects being mediated in extrastriate visual cortex, probably between visual areas V2 and MT [9]. In a second experiment in which the aftereffects were induced monocularly, their magnitudes were measured in the unadapted eye. Contraction effects transferred completely, suggesting that they are mediated by binocular cells. Expansion effects did not transfer completely, consistent with their having a monocular component. These data suggest that information about the orientation of axes-of-symmetry may be available as early as area V1, but that processing continues in extrastriate cortex.

Humans↗

PubMed1994

Modelling symmetry detection with back-propagation networks.

This paper reports experimental data and results of network simulations in a project on symmetry detection in small 6 x 6 binary patterns. Patterns were symmetrical about the vertical, horizontal, positive-oblique, or negative-oblique axis, and were viewed on a computer screen. Encouraged to react quickly and accurately, subjects indicated axis of symmetry by pressing one of four designated keys. Detection times and errors were recorded. Back-propagation networks were trained to categorize the patterns on the basis of axis of symmetry, and, by employing cascaded activation functions on their output units, it was possible to compare network performance with subjects' detection times. Best correspondence between simulated and human detection-time functions was observed after the networks had been given significantly more training on patterns symmetrical about the vertical and the horizontal axes. In comparison with no pre-training and pre-training with asymmetric patterns, pre-training networks with sets of single vertical, horizontal, positive-oblique or negative-oblique bars speeded subsequent learning of symmetrical patterns. Results are discussed within the context of theories suggesting that faster detection of symmetries about the vertical and horizontal axes may be due to significantly more early experience with stimuli oriented on these axes.

Computer Simulation↗