The structure of visual regularities

Contains fulltext : mmubn000001_444732144.pdf (publisher's version ) (Closed access)RU Radboud Universiteit Nijmegen, 22 november 2005Promotor : Weert, C.M.M. de Co-promotor : Helm, P.A. van der127 p

Helping elderly insomniacs get to sleep : the use of biofeedback relaxation exercises prompted by nocturnal sensing

No abstract

Helping elderly insomniacs get to sleep : the use of biofeedback relaxation exercises prompted by nocturnal sensing

No abstract

Sex differences in the detection of global and local visual regularities

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The force of symmetry revisited: Symmetry-to-noise ratios regulate (a)symmetry effects

Contains fulltext : 64504.pdf (publisher's version ) (Closed access)Freyd and Tversky’s [Am. J. Psychol. 97 (1984) 109] data suggested that human observers tend to overestimate relatively high levels of symmetry (symmetry effect), and tend to underestimate relatively low levels of symmetry (asymmetry effect). However, on the basis of their holographic approach to visual regularity, van der Helm and Leeuwenberg [Psychol. Rev. 103(3) (1996) 429] predicted that, at any level of symmetry, both symmetry and asymmetry effects may occur as a consequence of correct estimates of symmetry-to-noise ratios. This prediction was tested in two experiments, with tasks and stimuli similar to those in Freyd and Tversky’s study. First, subjects had to judge whether a noisy symmetry is more similar to a slightly more symmetrical variant or to a slightly less symmetrical variant. Second, for every pair of stimuli in such a triadic comparison, subjects had to judge which stimulus is the more symmetrical one. The results from both experiments show that the occurrence of (a)symmetry effects indeed depends on symmetry-to-noise ratios

Symmetry and repetition in perspective

Contains fulltext : 55307.pdf (publisher's version ) (Closed access)Although ecologically relevant, perspective views of symmetries and repetitions have hardly been investigated. Any symmetry or repetition that is not oriented orthogonally to the line of sight yields perspective distortions on the retina. In this study, these distortions are analyzed in terms of first-order structures (i.e., virtual lines between corresponding points) and second-order structures (i.e., correlation quadrangles formed by two virtual lines). In the literature, these structures have been proposed to guide the detection of frontoparallel symmetry and repetition. But what about perspective views? First, the analysis in this study shows that perspective distorts the retinal first-order and second-order structures of symmetry and repetition differently. Second, the results of two experiments on this distortion difference suggest that, in perspective views, symmetry and repetition detection is not preceded by normalization but occurs directly on the basis of the retinal first-order and second-order structures

Signal-to-noise ratio as a crucial determinant of vertical symmetry detection

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Measuring emotional wellbeing with a non-intrusive bed sensor

We examine the possibility of using non-intrusive bed sensor measures to ascertain the emotional wellness of an individual. To this end we did a convergent validation study to determine whether heart rate and respiration measures provided by the bed sensor correlate with self reports through questionnaires. The results show that negative affect and worry tension positively correlate with nocturnal respiration

Interactions between constituent single symmetries in multiple symmetry

Item does not contain fulltextAs a rule, the discriminability of multiple symmetries from random patterns increases with the number of symmetry axes, but this number does not seem to be the only determinant. In particular, multiple symmetries with orthogonal axes seem better discriminable than multiple symmetries with nonorthogonal axes. In six experiments on imperfect two-fold symmetry, we investigated whether this is due to extra structure in the form of so-called correlation rectangles, which arise only in the case of orthogonal axes, or to the relative orientation of the axes as such. The results suggest that correlation rectangles are not perceptually relevant and that the percept of a multiple symmetry results from an orientation-dependent interaction between the constituent single symmetries. The results can be accounted for by a model involving the analysis of symmetry at all orientations, smoothing (averaging over neighboring orientations), and extraction of peaks

Effects of asynchrony on symmetry perception,Psychologische Forschung

Item does not contain fulltextThe effect of temporal image segmentation on symmetry perception was investigated by means of stimuli composed of one part surrounding another. The two parts could be presented synchronously or with a temporal offset (20-100 ms), and each part could be either symmetrical or random. The task was to discriminate completely symmetrical (S) stimuli (in Experiment 1) or completely random (R) stimuli (in Experiment 2) from partially symmetrical (PS) stimuli in which one part was symmetrical and the other random. The R stimuli showed an asynchrony effect but the S stimuli did not. Furthermore, in both experiments, the PS stimuli showed an asynchrony effect when the symmetrical part was presented last but not when the symmetrical part was presented first (independent of whether it was the surrounded part or the surrounding part). Both results suggest that symmetry is strong enough to override this kind of temporal image segmentation.8 p