Visual Perception

By Silvia Gabrielli. Encyclopedia of Database Systems, 2018

617 citations recorded by the source corpus.

of 24.2) and 10 old (mean age of 71.4) partlclpants were shown with a short version of the psychophysical paradigm proposed by Pokorny and Smith (1997 Journal of the Optical Society of America), to bias processing toward MC or Pc. Observers had to discriminate the location of the higher luminance square within a four square stimulus array presented for 33 ms. In the steady pedestal condition (MC-bias), the array was preceded and followed by a four-identical-squares pedestal whereas, in the pulse pedestal condition (PC-bias), the array was presented alone. Two target luminance discrimination thresholds were collected for each experimental condition (3 pedestal-contrasts x 2 conditions) using an adaptive staircase procedure. The results showed a higher increase of threshold with pedestal contrast in the pulse relative to the steady condition. Moreover, a double interaction between group, pedestal contrast, and condition was observed: the rise in discrimination threshold found for old relative to young participants was higher in the pulse than in the steady pedestal conditions, especially for high pedestal contrasts. These results replicate the dissociation between the two low-level visual systems and demonstrate both a slight MC and a large PC impairment with normal ageing. for display size effects. The implications for models of search will be discussed. Visual search Little is known about visual search for targets on natural, textured backgrounds, or about the capacity of biological camouflage patterns to provide protection across a range of backgrounds. The experiments described address both these problems. Observers searched under diffuse day- light for a camouflaged target on a flat, natural surface, subtending approximately 35 x 20 0, while wearing a lightweight portable eye tracker. The targets were life-size images of four different moth species, varying in luminance contrast and size of pattern elements. They were printed on paper and,cut out. Two backgrounds were approximately uniform in colour (paving slabs, stucco wall), while two consisted of distinct objects varying in colour (stone chips, dead leaves). The identity, position, and orientation of the target varied randomly between trials. The background had a significant effect on search time, which was longest for the stucco wall, and shortest for the paved surface. The rank ordering of difficulty of search on the four backgrounds could not be explained by differences in first-order properties (mean luminance, contrast) between their images and those of the moths, nor by the strength of luminance gradients at the outlines of the moths. The results suggest that search follows segregation of a scene into distinct solid elements. vision in parallel with object segregation. We present a low-level geometry model based on a single type of self-adjusting grouping cell, with a circular array of dendrites connected to edge cells located at several angles. Different angles between active edge cells allow the grouping cell to detect geometric primitives like corners, bars and blobs. Such primitives forming different configurations can then be grouped to identify more complex geometry, like object shapes, without much additional effort. The speed of the model permits it to be used for fast gist vision, assuming that edge cells respond to transients in colour, texture, disparity and motion. The big single session of training. It has been reported that when a search display presented on one trial is predictive of the target's location on the next trial, reaction time (RT) for the next trial is improved. Here, we studied the effect of association across consecutive visual search trials on number of contexts which one can learn in a single session of training. We trained subjects to learn 12, 18, or 24 repeated displays in a single session, in which the spatial context on trial N - 1 was reliably followed by a specific target location on trial N. Results showed subjects' RT became significantly faster in all groups as the experiment. There was a significant difference between mean RTs of the experiments in which context N - 1 was predictive of target location on trial N and the control groups in which there was no association between trials, during training phase. We conclude that spatial contextual memory may benefit from the association across consecutive spatial contexts to improve context learning. Our (i) with duration 150-450 (ii) relatively independent of the (iii) straight jittered ortho-trajectory when step size was high and longer than 30 min of arc. signal line speed and length, but was not affected by duration severely by These that discrimination

Subfields: Social Psychology

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