![]() The standard deviation of the fit to the average data was 0.26. ( C) Psychometric functions for judging expression as a function of morph strength, using stimuli sampled at half-scale: the 0 and 1 strengths were the same as 0.25 and 0.75 in B. The standard deviation of the fit to the average data was 0.15. ( B) Psychometric functions for judging expression as a function of morph strength. The standard deviation of the fit to the average data was 0.32. The responses were fitted with cumulative Gaussian functions (colour-coded). Open black circles with black psychometric function show average data, coloured squares data divided according to the morph-strength of the previous trial (orange 1 green 0.75 red 0.5 blue 0.25 magenta 0). ( A) Psychometric functions for judging gender as a function of morph strength. ![]() Serial dependencies in judging gender and expression. Although integration could be important for expression, it is also essential to differentiate successive images, to maximize the detection of change. Expressions, on the other hand, are changeable, typically lasting between 0.5 and 4 seconds 21 and important information is conveyed in the change. Gender is a stable attribute, which should not change with successive viewings and should integrate. We tested this idea with perception of human faces, investigating, at the same time, perception of gender and expression. But do they also depend on the type of information being encoded? For example, attributes that tend to be stable over time may be more prone to integration, while for changeable attributes, the system may gain more from contrastive adaptation to maximize sensitivity to change, especially if the change is functionally important. What determines whether assimilation or contrastive effects prevail and how do the two opposing mechanisms interact? One factor is certainly stimulus conditions: strong, salient, high-contrast, long-duration stimuli tend to lead to negative aftereffects, while brief, less salient low-contrast stimuli lead to positive aftereffects 18, 19, 20. More recently, serial dependencies have been measured more directly, showing that the current image is often biased towards the previous, in orientation 14, numerosity 15 facial identity 16 and, most recently, pulchritude 17. ![]() Repetition priming is a well known effect in perception of faces 9 and many other attributes 10, 11, 12, 13. Positive serial dependencies between successive images have been observed for some time. On the other hand, in a constant but noisy environment, the system can profit by integrating successive views of images, which would produce positive rather than negative serial dependencies. ![]() Adaptation has been observed both for basic visual attributes, such as motion 3 and orientation 4 and also for more complex representations, such as numerosity 5 and faces 6, 7, 8. Adaptation to the prevailing level of any attribute – which leads to negative aftereffects – is thought to be a core mechanism for optimizing sensitivity to change 1, 2. The results point to highly sophisticated mechanisms for optimizing use of past information, either by integration or differentiation, depending on the permanence of that attribute.ĭetecting change, particularly in facial expression, is fundamental for perception. We found strong and consistent positive serial dependencies for gender and negative dependency for expression, showing that both processes can operate at the same time, on the same stimuli, depending on the attribute being judged. ![]() Subjects viewed a sequence of images varying simultaneously in gender and expression and scored each as male or female, and happy or sad. We reasoned that for stable attributes, such as the identity and gender of faces, the system should integrate: while for changeable attributes like facial expression, it should also engage contrast mechanisms to maximise sensitivity to change. Both processes occur in human vision, under different circumstances: they have been termed priming, or serial dependencies, leading to positive sequential effects and adaptation or habituation, which leads to negative sequential effects. Perceptual systems face competing requirements: improving signal-to-noise ratios of noisy images, by integration and maximising sensitivity to change, by differentiation. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |