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Biomedical subjects

R Röhler

Publications and source records attributed to R Röhler.

At least 19 recordsLinked to original sources

Lateral information transfer across saccadic eye movements.

Our perception of the visual world remains stable and continuous despite the disruptions caused by retinal image displacements during saccadic eye movements. The problem of visual stability is closely related to the question of whether information is transferred across such eye movements--and if so, what sort of information is transferred. We report experiments carried out to investigate how presaccadic signals at the location of the saccade goal influence the visibility of postsaccadic test signals presented at the fovea. The signals were Landolt rings of different orientations. If the orientations of pre- and postsaccadic Landolt rings were different, the thresholds of the test signals were elevated by about 20%-25% relative to those at the static control condition. When the orientations were identical, no such elevation occurred. This selective threshold elevation effect proved to be a phenomenon different from ordinary saccadic suppression, although it was closely related to the execution of the saccadic eye movement. The consequences for visual stability are discussed.

Adult↗

Evidence on the local character of spatial frequency channels in the human visual system.

The question has been raised as to whether there exists any transfer of information between neighboring retinal areas following presentation of spatially limited optical stimuli. Our experiments were aimed at mechanisms by which spatial frequency information could be transferred from one part of the visual field to another. Within a 0.9 degree X 2.5 degree section of the 3.6 degree X 2.5 degree testfield the observers adapt to a number of moving sinusoidally-modulated brightness or hue gratings of different spatial frequencies. As known by many publications the sensitivity to spatial frequencies changes in the adapted area. We find that this influence on the contrast threshold decreases as the distance to the adaptation section increases. Hence our results suggest mechanisms within the visual system mathematically best described by a local spectrum analysis.

Adaptation, Ocular↗

Sensitivity variations in the visual system, contrast resolution and eye movements.

Attention is drawn to the fact that under normal visual conditions the sensitivity of the receptor units of the visual system are subject to spatial and temporal variations, and that consequently in performing pattern recognition the visual cortex has to discriminate between external luminance structure and internal sensitivity structure. It is suggested that eye movements are the method by which this discrimination is performed. In a simplified model analysis it is shown that eye movements are a suitable mechanism for this discrimination. Implications of this model for detection threshold and stabilized retinal images are discussed. A new interpretation of the adaptation to sine wave grids is given.

Eye Movements↗