Biomedical subjects

E De Haan

Publications and source records attributed to E De Haan.

7 recordsLinked to original sources

PubMed2000

Interactions between exogenous auditory and visual spatial attention.

Six experiments were carried out to investigate the issue of cross-modality between exogenous auditory and visual spatial attention employing Posner's cueing paradigm in detection, localization, and discrimination tasks. Results indicated cueing in detection tasks with visual or auditory cues and visual targets but not with auditory targets (Experiment 1). In the localization tasks, cueing was found with both visual and auditory targets. Inhibition of return was apparent only in the within-modality conditions (Experiment 2). This suggests that it is important whether the attention system is activated directly (within a modality) or indirectly (between modalities). Increasing the cue validity from 50% to 80% influenced performance only in the localization task (Experiment 4). These findings are interpreted as being indicative for modality-specific but interacting attention mechanisms. The results of Experiments 5 and 6 (up/down discrimination tasks) also show cross-modal cueing but not with visual cues and auditory targets. Furthermore, there was no inhibition of return in any condition. This suggests that some cueing effects might be task dependent.

Adult↗

PubMed1996

The lateralization of lip-reading: a second look.

Photographs of unfamiliar speaking faces were matched by normal right-handed subjects on the basis of perceived mouth-shape (i.e. visible speech sound) across different face-views. A clear left-hemisphere (RVF) processing advantage emerged, which was absent when the task was that of identity matching. In contrast to earlier proposals, the extraction of lip-shape from face photographs may be better managed by left-hemisphere- than right-hemisphere mechanisms even at its initial stages. This may contribute to the observed patterns of dissociations in speech-reading and in audiovisual speech-processing in neurological patients.

Adult↗

PubMed1995

Shape from shaded random surfaces.

The perception of surface relief from random shading patterns is measured by having observers adjust three-dimensional local probes, the projections of which are superimposed on the image. Three observers perform four settings of 91 probes on each of 14 images. These images are generated by calculating the Lambertian reflectance of a random superposition of elliptical Gaussian hills and valleys illuminated by a single distant light source as well as by ambient light. Neither the surface reflectance equation nor the light source direction is conveyed to our observers in any way. Mathematically, this "pure" shape-from-shading problem has highly non-unique solutions. Perception of a well-defined, stable shape therefore implies that the ambiguity is resolved, i.e. a gauge is fixed. We analyse the surface ambiguity or gauge freedom which is left unconstrained by pure shading information and we investigate possible ways of restricting it. Statistical analysis of the curl component of the field of probe settings reveals that the settings are significantly consistent with an underlying perceived surface. In spite of the large theoretical ambiguity in the stimuli, the settings are reproducible and show considerable inter-observer agreement. Even the correlation of the settings with the real surfaces is surprisingly large. If the settings are compared to the real surface normals, one finds a series of biases, the strongest of which is that the global surface slant is systematically underestimated, even in those cases where ending occluding contours or high-contrast luminance ridges, indicative of "almost" contours, are present in the image. Another bias then is that the corresponding rims on the surface are seen as roughly parallel to the picture plane.

Cues↗

PubMed1994

Rapid segmentation of one-dimensional noise textures across borders.

We investigated the segmentation of texture pairs that were samples of one-dimensional binary visual noise. The stimulus consisted of an array of 5 x 8 squares separated by two-dimensional noise borders of varying width. The squares were filled with vertical black or white stripes of random width. The task was to detect the presence of a target square which differed from the squares above and below in one of three possible ways: the target pattern was either a contrast inverted copy or a horizontal translation of the pattern in the vertically adjacent squares, or else an independent realization of the noise. The binary noise in the textures was sequentially high-pass filtered to preclude the use of coarse-scale receptive fields and minimize the presence of sparse, extended "features". The target could be detected reliably within 100 msec even when the border width was larger than the maximal stripe width. The border width at threshold saturated for longer presentation times. Our results show that the microstructure of the patterns, i.e. information on the scale of the linewidth in the patterns, is not used directly, even though it contains most of the signal energy and is objectively the most reliable cue to the segmentation.

Contrast Sensitivity↗

PubMed1992

Selective loss of imagery in a case of visual agnosia.

Experiments were designed to examine the imagery abilities of an agnosic patient, M.S., who has consistently shown more severe deficits in recognizing visually, and in retrieving knowledge of living as compared with non-living items. Judgements of visual similarity were required for named objects and for object-pictures, as well as for the factual properties of these stimuli. The same disproportionate difficulty in processing living ('natural') objects was found in these tasks as well as in forced-choice recognition. In contrast, no deficit was found on analogous tasks concerned with word-shape similarities. These findings have a bearing on concepts of semantic memory.

Adult↗

PubMed1989

Implicit access to semantic information.

Three experiments investigating the patient M.S.'s semantic memory are reported. Experiments 1 and 2 involved a category-membership decision task, in which M.S. was asked to determine whether a noun was a member of a specified semantic category. His performance in Experiment 1 was impaired for nouns from living categories in comparison with nouns from nonliving categories, and this impairment was especially marked for nouns of low typicality. Experiment 2 demonstrated an equivalent pattern of very poor performance to nouns of low familiarity from living categories. In Experiment 3 the effect of a category label on lexical decision was examined, using category labels as primes preceding nouns or pronounceable nonwords. Facilitation from related category label primes was found for typical and untypical members of living and nonliving semantic categories. These findings demonstrate that M.S. has impaired knowledge of the structure of living semantic categories when explicit access to this information is required (Experiments 1 and 2), but that some form of preserved category structure can be demonstrated in tasks which assess this implicitly (Experiment 3).

Agnosia↗

PubMed1987

Exposure and response prevention in patients with obsessions.

The outpatient treatment of patients with obsessions alone is often said to be less successful compared to the outpatient treatment of patients with both obsessions and compulsive symptoms. This article presents the outcome of the treatment of 26 obsessive patients. The success rate, measured after 10 treatment sessions, was 73%. At follow-up after 12-36 months, improvement appeared to have been maintained or to have increased in 61.5% of the patients, figures comparable to the outcome of patients with both obsessions and compulsions.

Adolescent↗