Biomedical subjects

E Blaser

Publications and source records attributed to E Blaser.

12 recordsLinked to original sources

PubMed2000

Tracking an object through feature space.

Visual attention allows an observer to select certain visual information for specialized processing. Selection is readily apparent in 'tracking' tasks where even with the eyes fixed, observers can track a target as it moves among identical distractor items. In such a case, a target is distinguished by its spatial trajectory. Here we show that one can keep track of a stationary item solely on the basis of its changing appearance--specified by its trajectory along colour, orientation, and spatial frequency dimensions--even when a distractor shares the same spatial location. This ability to track through feature space bears directly on competing theories of attention, that is, on whether attention can select locations in space, features such as colour or shape, or particular visual objects composed of constellations of visual features. Our results affirm, consistent with a growing body of psychophysical and neurophysiological evidence, that attention can indeed select specific visual objects. Furthermore, feature-space tracking extends the definition of visual object to include not only items with well defined spatio-temporal trajectories, but also those with well defined featuro-temporal trajectories.

Attention↗

PubMed2000

Color-specific depth mechanisms revealed by a color-contingent depth aftereffect.

Models of stereoscopic depth perception for both natural and random-dot images have focused mainly on the matching of achromatic features of binocular images. Recently, a growing body of research has investigated whether chromatic features can also contribute to the construction of stereoscopic depth. Here we present experiments yielding color-contingent depth aftereffects comparable in magnitude to those measured after adaptation to achromatic stimuli as evidence of neural mechanisms tuned to both color and depth. Furthermore, we report that the locus of the combined processing of color and depth is likely to lie beyond the site of binocular matching.

Adaptation, Physiological↗

PubMed1999

Measuring the amplification of attention.

An ambiguous motion paradigm, in which the direction of apparent motion is determined by salience (i.e., the extent to which an area is perceived as figure versus ground), is used to assay the amplification of color by attention to color. In the red-green colored gratings used in these experiments, without attention instructions, salience depends on the chromaticity difference between colored stripes embedded in the motion sequence and the yellow background. Selective attention to red (or to green) alters the perceived direction of motion and is found to be equivalent to increasing the physical redness (or greenness) by 25-117%, depending on the observer and color. Whereas attention to a color drastically alters the salience of that color, it leaves color appearance unchanged. A computational model, which embodies separate, parallel pathways for object perception and for salience, accounts for 99% of the variance of the experimental data.

Attention↗

PubMed1995

The accuracy and precision of saccades to small and large targets.

Subjects made saccades to point and spatially-extended targets located at a randomly-selected eccentricity (3.8-4.2 deg) under conditions designed to promote best possible accuracy based only on the visual information present in a single trial. Saccadic errors to point targets were small. The average difference between mean saccade size and target eccentricity was about 1% of eccentricity. Precision was excellent (SD = 5-6% of eccentricity), rivaling the precision of relative perceptual localization. This level of performance was maintained for targets up to 3 deg in diameter. Corrective saccades were infrequent and limited almost exclusively to the point targets. We conclude that the saccadic system has access to a precise representation of a central reference position within spatially-extended targets and that, when explicitly required to do so, the saccadic system is capable of demonstrating remarkably accurate and precise performance.

Female↗

PubMed1995

The role of attention in the programming of saccades.

Accurate saccadic programming in natural visual scenes requires a signal designating which of the many potential targets is to be the goal of the saccade. Is this signal controlled by the allocation of perceptual attention, or do saccades have their own independent selective filter? We found evidence for the involvement of perceptual attention, namely: (1) summoning perceptual attention to a target also facilitated saccades; (2) perceptual identification was better at the saccadic goal than elsewhere; and (3) attempts to dissociate the locus of attention from the saccadic goal were unsuccessful, i.e. it was not possible to prepare to look quickly and accurately at one target while at the same time making highly accurate perceptual judgements about targets elsewhere. We also studied the trade-off between saccadic and perceptual performance by means of a novel application of the "attentional operating characteristic" (AOC) to oculomotor performance. This analysis revealed that some attention could be diverted from the saccadic goal with virtually no cost to either saccadic latency or accuracy, showing that there is a ceiling on the attentional demands of saccades. The links we discovered between saccades and attention can be explained by a model in which perceptual attention determines the endpoint of the saccade, while a separate trigger signal initiates the saccade in response to transient changes in the attentional locus. The model will be discussed in the context of current neurophysiological work on saccadic control.

Attention↗

PubMed1993