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R Groner

Publications and source records attributed to R Groner.

9 recordsLinked to original sources
PubMed1997

Backward masking of words and faces: evidence for different processing speeds in the hemispheres?

Two tachistoscopic experiments with a lateralized presentation of function words and faces were carried out to investigate the influence of temporal factors and type of masking on visual field asymmetries. Accuracy, represented by signal detection measures (d' and beta), was calculated separately for the two visual fields, for various interstimulus intervals, and for noise and pattern masking. In both experiments, d' increased with prolonged temporal delay between target and mask. In the lexical decision task, visual field interacted with mask type confirming that only in the pattern mask condition did an advantage of the right visual field emerge. In the facial decision task, however, visual field interacted with interstimulus interval, confirming that, in the left visual field, the facial information escaped the masking effect earlier than in the right visual field. In the facial task, there was a higher response criterion (beta) in the left visual field. By applying different types of masks, visual processing of lexical stimuli can be disrupted at distinct stages where perceptual asymmetries are present to a varying extent. The results of both experiments suggest that words and faces are differentially affected by masking procedures.

Adult↗
PubMed1996

Visual field asymmetries in schematic persistence.

A modified partial-report technique was used as a tool to study hemispheric asymmetries in schematic persistence. Two types of stimuli were presented: (1) verbal stimuli consisting of function words and nonsense words, and (2) pictures of faces and nonfaces. The stimulus items were arranged bilaterally in a circular array around the fixation point and the participants' task was to decide whether the probed item was a correct or distorted version of each stimulus type. Delay time between stimulus set and marker ranged from 0 ms to 360 ms. Calculating a sensitivity measure of accuracy, distinctive visual field differences emerged which depended on the nature of the stimuli; that is, a left field advantage for facial stimuli and a right field advantage for lexical stimuli. In addition, performance decreased linearly as delay time between probe and marker increased. The present results indicate that on a level of schematic persistence perceptual hemispheric asymmetries are already strongly present.

Journal Article↗
PubMed1996

Eye movement modifies motion trajectory of a moving target.

Smooth pursuit eye movements have strong modulating effects on perceived motion both temporally and spatially. Abrupt changes in the direction of a target cause non-veridical perceived velocity and trajectory pattern when a visual cues appear with the moving target. In addition, this condition of non-veridical velocity and trajectory perception increases no visual cues are presented. Non-veridical perception was also connected with target velocity: the more difficult the eye pursuit, the more frequent was the non-veridical perception.

Acceleration↗
PubMed1993

On the confounding effects of phosphor persistence in oscilloscopic displays.

Phosphor persistence has been a source of confounding in studies of temporal integration in vision. We examined the confounding by assessing the effects of the persistence of two commonly-used phosphors (P15 and P31) on performance of a temporal-integration task. In one experiment we eliminated the visibility of phosphor persistence by closing two mechanical shutters upon display termination. In a second experiment we estimated the duration of phosphor persistence by displaying the image behind closed shutters which opened upon display termination. No detectable persistence was every produced by P15 phosphor. By contrast, P31 phosphor produced persistence that lasted several hundred milliseconds even when a veiling light was projected on the screen. We ascribe the earlier instances of confounding to inadequate interpretation of the technical data on phosphor decay.

Humans↗
PubMed1992

Specific effects of the benzodiazepine midazolam on visual receptive fields in light and dark adapted human subjects.

Psychophysical experiments in humans have revealed similar characteristics of visual receptive fields as were found in cats and monkeys from retinal ganglion cell recordings. In addition, in some retinal ganglion cells of cats the GABA antagonist bicuculline decreases the activity of the inhibitory surround. These findings led to two predicitions: 1) benzodiazepines will selectively increase the inhibitory surround of human visual receptive fields, 2) after dark adaptation, no free GABA will be available in the synapses and benzodiazepines will have no effect on the visual system. Characteristics of human receptive fields were determined by subthreshold summation: the contrast threshold of a vertical line was measured dependent on the distance of two parallel flanking lines whose contrast was below threshold. Both hypotheses were confirmed: the threshold in the inhibitory region of receptive fields was specifically increased in a dose-dependent manner by midazolam PO (7.5 mg: P < 0.05; 15 mg: P < 0.01). In dark-adapted subjects no effect of midazolam was found. Control experiments with atropine (1 mg IV), sulpiride (100 mg IM), and levodopa (100 mg PO) showed no specific effect. The visual system may be a model to bridge the gap between animal and human psychopharmacology.

Adaptation, Ocular↗
PubMed1989

Attention and eye movement control: an overview.

A review of recent experimental and theoretical findings is presented which relates the results of neurophysiological and psychological research on attention and eye movement to cognitive theorizing. With respect to the relation between shifts of attention and saccadic eye movements, several experiments have demonstrated that it is possible to dissociate the line of attention from the gaze direction. On the other hand, there is some indirect (although not yet conclusive) evidence that saccadic eye movements always produce a concomitant shift of attention. Another question is whether there is a moment-to-moment control of each consecutive saccade and latency or whether indirect control models (i.e. planning several saccades in advance) are more appropriate. The function of attentional processes which have to coordinate stimulus driven (bottom-up) and concept driven (top-down) mechanisms are discussed and related to some studies investigating local and global scanpaths.

Attention↗
PubMed1983

Influence of diazepam and methylphenidate on identification of rapidly presented letter strings: diazepam enhances visual masking.

The effect of diazepam (0, 5, 10 mg) and methylphenidate (0, 5, 10 mg) on the identification of briefly displayed letter strings composing words was investigated. Each letter was presented for 70 ms. The interstimulus interval (ISI) between two successive letters was 10, 100 or 200 ms. The length of the words (WL) was three, five, seven or nine letters. The dependent variable was the number of correctly identified words. As predicted, strong visual masking effects, the strength of which was dependent on ISI and WL, appeared. In the 10 ms condition, diazepam at both doses, but not methylphenidate, further enhanced masking. It is suggested that the results reflect the effect of GABA on masking, and support certain psychological theories about the inhibitory neuronal pathways that are involved in masking. The human peripheral visual system is a promising model for the experimental assessment and integration of pharmacodynamic, neurophysiological and psychological observations.

Adult↗