Biomedical subjects

Dieter Heller

Publications and source records attributed to Dieter Heller.

7 recordsLinked to original sources

PubMed2004

On the relations between crowding and visual masking.

To study the question of which processes contribute to crowding and whether these are comparable to those of visual temporal masking, we varied the stimulus onset asynchrony (SOA) between target and flankers in a crowding setting. Monotonically increasing Type A masking functions observedfor small spacings and large eccentricities indicate that the integration of information from target and flankers underlies crowding. Decreasing masking functions obtained for large spacings and small eccentricities relate processes of crowding to those contributing to Type B masking. In addition, Type B masking was more frequent with letter-like nonletter flankers than with letter flankers, suggesting that Type B masking, just like crowding over large areas, is due to higher level interactions. The rapid decrease of the effects of interletter spacing and eccentricity with increasing SOA indicates that positional information is transient.

Fixation, Ocular↗

PubMed2004

Phonological representation of words in working memory during sentence reading.

The temporal dynamics of a visual target word's phonological representation was examined by presentation of an irrelevant spoken companion word when the participant's eyes reached the target's location during sentence reading. The spoken word was identical, similar, or dissimilar to the phonological specification of the visual target. All spoken words increased the time spent viewing the target, with larger effects in the similar and dissimilar spoken word conditions than in the identical condition. The reading of posttarget text was disrupted when the spoken word was similar but not when it was identical or dissimilar to the target. Phonological interference indicates that a word's phonological representation remains active after it has been identified during sentence reading.

Eye Movements↗

PubMed2003

Dodge-ing the issue: Dodge, Javal, Hering, and the measurement of saccades in eye-movement research.

Dodge, in 1916, suggested that the French term 'saccade' should be used for describing the rapid movements of the eyes that occur while reading. Previously he had referred to these as type I movements. Javal had used the term 'saccade' in 1879, when describing experiments conducted in his laboratory by Lamare. Accordingly, Javal has been rightly credited with assigning the term to rapid eye movements. In English these rapid rotations had been called jerks, and they had been observed and measured before Lamare's studies of reading. Rapid sweeps of the eyes occur as one phase of nystagmus; they were observed by Wells in 1792 who used an afterimage technique, and they were illustrated by Crum Brown in 1878. Afterimages were used in nineteenth-century research on eye movements and eye position; they were also employed by Hering in 1879, to ascertain how the eyes moved during reading. In the previous year, Javal had employed afterimages in his investigations of reading, but this was to demonstrate that the eyes moved horizontally rather than vertically. Hering's and Lamare's auditory method established the discontinuous nature of eye movements during reading, and the photographic methods introduced by Dodge and others in the early twentieth century enabled their characteristics to be determined with greater accuracy.

Biomedical Research↗

PubMed2003

Visual motion illusions, eye movements, and the search for objectivity.

The initial interpretations of motion phenomena are often in terms of eye movements. It reflects a desire to link an objective expression of motion (of the eyes) with a subjective experience of motion. This approach is examined historically with respect to induced motion, motion aftereffects, visual vertigo, autokinetic effects and stroboscopic motion. All but one of these phenomena were initially observed in the natural environment and they have subsequently been studied under laboratory conditions. Eye movements are not correlated with induced motion, the motion aftereffect, or stroboscopic motion, but they do correspond to the direction and extent of visual vertigo. The extent of apparent visual motion in the autokinetic effect far exceeds that of involuntary eye movements but there might be a weak relation between them. If eye movements are to provide a reasonable account of motion illusions then they should apply to all the contours that are visible. This does apply to visual vertigo, but not to induced motion, the motion aftereffect and stroboscopic motion, all of which involve relative motion in a visible display. The autokinetic phenomenon involves the perception of isolated stimuli, and so interpretations in terms of some internal eye movement signals remain sustainable.

Eye Movements↗

PubMed2002

Spatial selection in peripheral letter recognition: in search of boundary conditions.

Recognition performance for a peripherally presented target letter embedded in a letter string is worse than for targets presented in isolation. This lateral masking effect is commonly attributed to impairments when identifying flanked letters. The hypothesis that also failures during spatial selection of the target underlie lateral masking effects was examined by varying the brightness of the flankers (Experiment 1), by cueing the target position at various times before, during, or after presentation of the string (Experiment 2) and by avoiding the abrupt on- and offset of the flankers (Experiments 3 and 4). Whereas the flankers' brightness had no effect on and cueing only slightly reduced the lateral masking effects, it was substantially reduced by avoiding the abrupt on- and offset of the flankers. The results show that spatial selection is impaired in peripheral vision, and that this is one important factor underlying lateral masking effects.

Adult↗

PubMed2002

Visual search in long-term cannabis users with early age of onset.

The present research tested the hypothesis that there is a specific deficit in visual scanning in chronic users of cannabis with early onset of their drug consumption (age 14 to 16). 17 users and 20 control participants were asked to search for targets on a 5 x 5 stimulus array while their eye movements were monitored. Cannabis users showed less effective search behavior, including longer response times and more fixations at about the same error level. Search patterns were more conservative and included more frequent reinspections of previously fixated areas. In sum, the results point to two loci of adverse effects: an impairment in visual short-term memory, and less effective visual processing at a more strategic, top down controlled level.

Adult↗

PubMed2002

Visual search for dimensionally redundant pop-out targets: parallel-coactive processing of dimensions is location specific.

Three visual search experiments investigated redundancy gains for single and dual odd-one-out feature targets that differed from distractors in orientation, color, or both. In Experiment 1, redundant-target displays contained (a) a single target defined in 2 dimensions, (b) dual targets each defined in a different dimension, or (c) dual targets both defined in the same dimension. The redundancy gains, relative to single nonredundant targets, decreased from the first condition on, with violations of J. Miller's (1982) race model inequality (RMI) manifested only in the first 2 conditions. Experiment 2 systematically varied the spatial separation between dual targets each defined in a different dimension. Violations of the RMI were evident only when the 2 targets occupied nearby locations. Experiment 3 provided evidence of RMI violations by dimensionally redundant targets at both precued (likely) and noncued (unlikely) display locations. Taken together, these results suggest that there is coactivation of a common mechanism by target signals in different dimensions (not by signals in the same dimension), that the coactivation effects are spatially specific, and that the coactivated mechanisms are located at a preattentive, perceptual stage of processing.

Adult↗