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In the course of perceptual organization, incomplete optical stimulation can evoke the experience of complete objects with distinct perceptual identities. According to a well-known principle of perceptual organization, stimulus parts separated by shorter spatial distances are more likely to appear as parts of the same perceptual identity. Whereas this principle of proximity has been confirmed in many studies of perceptual grouping in static displays, we show that it does not generalize to perception of object identity in dynamic displays, where the parts are separated by spatial and temporal distances. We use ambiguous displays which contain multiple moving parts and which can be perceived two ways: as two large objects that gradually change their size or as multiple smaller objects that rotate independent of one another. Grouping over long and short distances corresponds to the perception of the respectively large and small objects. We find that grouping over long distances is often preferred to grouping over short distances, against predictions of the proximity principle. Even though these effects are observed at high luminance contrast, we show that they are consistent with results obtained at the threshold of luminance contrast, in agreement with predictions of a theory of efficient motion measurement. This is evidence that the perception of object identity can be explained by a computational principle of neural economy rather than by the empirical principle of proximity. [ABSTRACT FROM AUTHOR]

We adopted the psychological refractoriness paradigm to study whether visual pattern goodness affects central processing load in a same-different task. In a dual-task experiment, a two-alternative forced choice auditory classification was followed by a same-different task in which Garner's classical five-dot patterns were presented. Goodness of these patterns and stimulus-onset asynchrony (SOA) between the first and second task were varied between trials. Participants used a physical sameness criterion; only patterns of the same shape and orientation were responded to as same. Strong effects of pattern goodness and SOA were found, and both factors had additive effects on response latencies. This result was taken as evidence that pattern goodness determines central processing load in the physical sameness task. The result is consistent with Lachmann and van Leeuwen (2007a ), in which a categorical sameness task was used. Comparing both studies it was concluded that goodness reduces the central processing load of visual stimulus information independently of task variation. [ABSTRACT FROM AUTHOR]

Perceptual grouping is a multi-stage process, irreducible to a single mechanism localized anatomically or chronometrically. To understand how various grouping mechanisms interact, we combined a phenomenological report paradigm with high-density event-related potential (ERP) measurements, using a 256-channel electrode array. We varied the relative salience of competing perceptual organizations in multi-stable dot lattices and asked observers to report perceived groupings. The ability to discriminate groupings (the grouping sensitivity) was positively correlated with the amplitude of the earliest ERP peak C1 (about 60 ms after stimulus onset) over the middle occipital area. This early activity is believed to reflect spontaneous feed-forward processes preceding perceptual awareness. Grouping sensitivity was negatively correlated with the amplitude of the next peak P1 (about 110 ms), which is believed to reflect lateral and feedback interactions associated with perceptual awareness and attention. This dissociation between C1 and P1 activity implies that the recruitment of fast, spontaneous mechanisms for grouping leads to high grouping sensitivity. Observers who fail to recruit these mechanisms are trying to compensate by using later mechanisms, which depend less on stimulus properties such as proximity. [ABSTRACT FROM AUTHOR]

In three experiments, participants determined the orientation of a global triangle formed by three Gabor patches of a target spatial frequency in a field of distracters. The orientation of the target patches and their proximity were varied between conditions. When all the target patches had the same orientation this facilitated the response compared to random orientations. This effect occurred only when the patches were in close proximity. When the orientations of the target patches were different but aligned to the global triangle, facilitation occurred regardless of proximity. These contrasting types of facilitation were attributed to different early perceptual integration mechanisms that enable the perception of holistic structure. [ABSTRACT FROM AUTHOR]

We adopted the Psychological Refractoriness Paradigm to study whether perceptual Goodness affects the load of central processing resources. In three dual-task experiments, 2-Alternative Forced Choice auditory classification was followed by a same–different task in which Garner’s classical five-dot patterns were presented. Goodness of these patterns and stimulus-onset asynchrony (SOA) between the first and second task were varied between trials. These factors had additive effects on response latencies and accuracy, indicating that pattern Goodness determines central processing load in performing the same–different task. In a fourth experiment, same–different judgment with Garner patterns was the single task. SOA between the first and second pattern was varied. Over-additive effects of Goodness with decreasing SOA were obtained, indicating sharing of central resources between consolidation of the first Garner pattern and performing the same–different task. Whereas, the resources needed for the latter, again, depend on Goodness, those needed for consolidation are independent of it. [ABSTRACT FROM AUTHOR]

Perceptual experience cast be explained by contextualized brain dynamics. An inner loop of ongoing activity within the brain produces dynamic patterns of synchronization and de-synchronization that are necessary, but not sufficient, for visual experience. This inner loop is controlled by evolution, development, socialization, learning, task and perception-action contingencies, which constitute an outer loop. This outer loop is sufficient, but not necessary, for visual experience. Jointly, the inner and outer loop may offer sufficient and necessary conditions for the emergence of visual experience. This hypothesis has methodological, empirical, theoretical, and philosophical implications. [ABSTRACT FROM AUTHOR]

We studied context dependency of the representations underlying perceptual “goodness”. Three experiments used a same – different task with classical Garner 5-dot patterns presented with an interstimulus interval (ISI) of 500  ms. Same patterns were allowed to be rotated or reflected versions of each other. Pattern goodness was varied according to rotation and reflection equivalence, using GarneR&Rsquo;s equivalence set size (ESS) measure. The ESS of both first and second patterns affected reaction time and accuracy. A model based on assumptions that GarneR&Rsquo;s equivalence sets constitute the generic representation of these patterns and that items within these sets are accessed serially was fitted to the data. Excellent fits were obtained, which were robust against frequency-induced bias at the level of the individual pattern, but sensitive to such bias at the level of the equivalence set. It was concluded that individual pattern representations are context independent, whereas their collective representations are context dependent. Simplicity and likelihood principles, therefore, seem to apply to different levels of a representation hierarchy. [ABSTRACT FROM AUTHOR]

The author reflects on color and form perception. Topics discussed include neuroscience, visual information processing, and neural architecture. Also being discussed are broadband selectivity and population coding of sensory information; different tuning characteristics in color space; and developments in population coding.

We investigated the possible causes of perceptual switching in ambiguous figures. Ambiguous figures are a special class of visual stimuli that can give rise to at least two alternative interpretations. Because the figures themselves stay the same, these stimuli are particularly suitable to study the dynamic changes in our visual apparatus that enable us to see the world in different ways. Recent studies stress the importance of both low-level (sensory) and high-level (cognitive) processes in switching. We show that these processes lead to switching independently, and that, when they co-occur, they do not occur at exactly the same time. We take these results to indicate that perceptual switching is a radically multiply realizable process, in that various neurological states can instantiate it in a single individual from time to time. We reflect on the consequences of this conclusion for experiential realism, in particular the notion that embodiment misleads us in identifying psychological types. [ABSTRACT FROM AUTHOR]