Optimality of Human Contour Integration

For processing and segmenting visual scenes, the brain is required to combine a multitude of features and sensory channels. It is neither known if these complex tasks involve optimal integration of information, nor according to which objectives computations might be performed. Here, we investigate if optimal inference can explain contour integration in human subjects. We performed experiments where observers detected contours of curvilinearly aligned edge configurations embedded into randomly oriented distractors. The key feature of our framework is to use a generative process for creating the contours, for which it is possible to derive a class of ideal detection models. This allowed us to compare human detection for contours with different statistical properties to the corresponding ideal detection models for the same stimuli. We then subjected the detection models to realistic constraints and required them to reproduce human decisions for every stimulus as well as possible. By independently varying the four model parameters, we identify a single detection model which quantitatively captures all correlations of human decision behaviour for more than 2000 stimuli from 42 contour ensembles with greatly varying statistical properties. This model reveals specific interactions between edges closely matching independent findings from physiology and psychophysics. These interactions imply a statistics of contours for which edge stimuli are indeed optimally integrated by the visual system, with the objective of inferring the presence of contours in cluttered scenes. The recurrent algorithm of our model makes testable predictions about the temporal dynamics of neuronal populations engaged in contour integration, and it suggests a strong directionality of the underlying functional anatomy

A spatial explanation for synchrony biases in perceptual grouping: Consequences for the temporal-binding hypothesis

If two images are shown in rapid sequential order, they are perceived as a single, fused image. Despite this, recent studies have revealed that fundamental perceptual processes are influenced by extremely brief temporal offsets in stimulus presentation. Some researchers have suggested that this is due to the action of a cortical temporal-binding mechanism, which would serve to keep multiple mental representations of one object distinct from those of other objects. There is now gathering evidence that these studies should be reassessed. This article describes evidence for sensitivity to fixational eye and head movements, which provides a purely spatial explanation for the earlier results. Taken in conjunction with other studies, the work serves to undermine the current body of behavioral evidence for a temporal-binding mechanism

Simultaneous Synthesis of Al-Doped ZnO Nanoneedles and Zinc Aluminum Hydroxides through Use of a Seed Layer

Al-doped ZnO nanoneedles with a tip diameter of similar to 10 nm and hexagonal zinc aluminum hydroxide were simultaneously synthesized and completely separated in one step. An aqueous solution containing metal ions (Zn(2+) and Al(3+)), in which a Zn-deposited substrate was immersed, was irradiated with microwaves. Al-doped ZnO nanoneedles (average Zn/Al molar ratio of 55.5) grew on the substrate, whereas zinc aluminum layered double hydroxides (average Zn/Al molar ratio of 2.51) grew as homogeneous precipitates in the bulk solution. The ID Al-doped ZnO nanoneedles had an average length of similar to 1.3 mu m. The length, diameter, and shape of the nanoneedles were uniform. The 2D hexagonal zinc aluminum hydroxides had lateral dimensions of 500 nm to 1.8 mu m and an average thickness of similar to 50 nm. Asymmetric partitioning of Zn and Al species was observed in the simultaneous synthesis of these nano/microcrystalsclos