Session Detail

Nonlinear VEP has been used to separate magno and parvocellular contributions to the evoked potential, on the basis of contrast gain, amplitude saturation and latency. Here we studied MEG cortical multifocal responses to diffuse blue stimulation as a function of colour saturation. 9 university age students with normal colour vision participated. An m=14 pseudorandom stimulus sequence was applied to 8 segments each fluctuating between blue colour (95% 75% 50% 25% and 0% saturation) and an achromatic stimulus (grey) of higher luminance. An Elekta TRIUX MEG system recorded magnetic evoked fields. First and second order Wiener kernels were analysed using Brainstorm with data co-registered on 0.75mm isovoxel MRI images. While sensor cluster first order kernels showed some increase in amplitude with saturation, the greatest chromatic sensitivity was demonstrated by the N60P90 peak of the first slice of the second order response, whose amplitudes showed a roughly linear function of saturation across each of the four central stimulus quadrants. Initial minimum norm source estimates shows the main contribution to come from striate cortex. While such stimuli would be expected to reflect koniocellular function, further questions are posed by the short latencies recorded – similar to those attributed to magnocellular function.

 

Human observers perceive glossiness on object surfaces from rather low luminance regions without specular highlights (Kim et al., 2012). However, it has been unclear what image information was a cue for perceived glossiness based on low luminance regions. To examine this issue, we performed glossiness rating experiments using a number of computer-graphics images of objects with different shapes, reflectance properties, and light fields. There were two conditions about stimulus luminances: the normal condition in which computer-graphics images were directly used, and the no-highlight condition in which luminances of specular highlights were clipped. In the results, glossiness rating scores were higher in the no-highlight condition than the normal condition in some objects, demonstrating that low-luminance regions more strongly contribute to perceived glossiness than specular highlights in certain conditions. Furthermore, a Laplacian filter analysis showed that, on the objects on which the rating scores were higher in no-highlight condition, amounts of luminance edges on object surfaces were strongly correlated with the rating scores, while they were only weakly correlated on the other objects. These results suggest that luminance edge components on object surfaces are an effective cue for perceived glossiness even when high luminance regions do not exist.

 

Studies have shown that facial skin pigmentation is an important cue on human physical attraction judgement. However, little is known about how skin color information influences the perception of facial skin pigmented spot. We compared the visual perception of the facial skin pigmentation with various color density between two backgrounds, which are only different in color distribution. In a two-alternative forced choice paradigm, subjects were asked to judge the existence of a skin pigmented spot on a background image. The background image was a cheek picture or a random pixel image created from the same cheek picture. Stimuli were displayed for a period of 300 ms and followed by a mask with a period of 200 ms. Performance was tested with different pigmentation color density which was divided the distance between the facial skin and the pigmentation into equal 20 scales in the CIELAB Color Space. The result indicated that the performance of pigmented spot judgment increased with the increasing of the color density of the skin pigmentation. This result was only found when the pigmented spot appeared on the background of the cheek skin image, suggesting that a facial skin-color distribution plays an important role in face perception.