Laura Bamert
Self-Other Discrimination in a Hand Laterality Judgment Task
Authors
Laura Bamert (University of Lausanne)
Fred W. Mast (University of Lausanne)
The hand laterality judgment task implicitly requires mental rotation, and thus the results show a linear increase of reaction times as a function of stimulus rotation (Parsons, 1994). We examined the performance of adult subjects by using photographed pictures of their own hands and hands of people unknown to them. The hand stimuli were presented in eight different orientations in the picture plane, either in back view or palm view. For stimulus orientation, view (back or palm) and stimulus hand (left or right), the results are congruent with those found in previous experiments (e.g. Parsons, 1994): higher reaction times and error rates for left hands (all subjects were right-handed), for palm-viewed hands and for uncommon orientations. Interestingly, hand ownership interacted with stimulus orientation (clockwise; counter clockwise). This result suggests that the underlying motor rotation process is influenced when subjects view their own hand even though no explicit recognition is required when performing the hand laterality judgment task. Future studies will reveal more precisely the conditions under which the involvement of one’s own hand facilitates or interferes with task performance. These results are discussed with respect to the embodiment of imagined body part transformations.
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Joseph Krummenacher
Temporal Characteristics of Signal Integration in Cross-Modal Conjunction Search
Authors
Joseph Krummenacher (University of Fribourg)
Alain Chavaillaz (University of Fribourg)
In a recent investigating of the temporal characteristics of feature processing in visual search for conjunction targets, the colour and form features of display objects were changed in sequential order. Using various feature change asynchronies (FCA), colour changes could be followed by form changes and vice versa. The results showed that reaction times were slowest if the two feature changes occurred simultaneously (FCA=0). Different explanations were proposed to account for this finding, including a refractory period, and, alternatively, statistical interference of the two signals.
We report a study aimed at deciding between those two possible explanations using conjunctions of visual, auditory, and tactile stimuli. The rationale of the experimental setup was that visual-visual conjunctions might result in a type of interference that is not observed if different modalities are involved in the conjunction task. The results suggest the existence of different types of modality-dependent interference patterns.
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Marcello Indino
Development of Dimensions-based Processing in Visual Search in Children
Authors
Marcello Indino (University of Zurich)
Friedrich Wilkening (University of Zurich)
Although visual search for targets that differ from distractors in a salient feature is fast and efficient, reaction times are affected by changes in the target-defining dimension (e.g. colour, orientation) across trials. Reaction times are speeded if the target dimension is repeated from a previous to a current trial; they are slower if the feature changes, however. The precise cognitive function of these reaction time costs and benefits remains unclear. To exaggerate: is it a feature of the visual processing system or a bug in it. One approach of assessing the functional role (significance) of the dimension change effects is in investigation samples of children of different ages in order to establish whether they are observed in children of any age category or whether it emerges gradually or whether it is related to a specific developmental step.
We present the development of search displays containing visual stimuli taken from the experiential world of children of various age ranges which currently allow us to investigate in detail the development of dimension-based reaction time patterns.
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Michael H. Herzog
Top-down and bottom-up processing in perceptual learning
Authors
Michael H. Herzog (Swiss Federal Institute of Technology Zurich )
Kristoffer Åberg (Swiss Federal Institute of Technology Zurich)
Elisa Tartaglia (Swiss Federal Institute of Technology Zurich)
Perceptual learning is the ability to learn to perceive something new. Perceptual learning has gained increasing interest in the last 20 years. Still, the underlying mechanisms are largely unknown. We will first give an overview of open questions in perceptual learning and then focus on the interesting phenomenon of roving: no learning occurs when different stimuli are presented randomly interleaved- even though performance on each stimulus improves when training with the stimuli was in separate sessions, i.e. one stimulus after the other. We will characterize for which pairs of stimuli roving occurs and for which it does not, i.e. when performance improves also for interleaved stimulus presentations. We will discuss the role of bottom up versus top-down processing in roving conditions concluding with some general considerations on models of perceptual learning.
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Dirk Kerzel
Attentional selection for perception is under voluntary control
Authors
Dirk Kerzel (University of Geneva)
Leily Zarian (University of Geneva)
David Souto (University of Geneva)
Previous studies have demonstrated that a brief visual transient improves perceptual discrimination of subsequent stimuli. For instance, participants are able to indicate the orientation of a grating more reliably if a flash is presented above the grating about 120 ms before the onset of the grating. Studies reporting such cueing benefits on perception used cues that predicted the location of the target. For instance, when the flash was presented on the right, the target would have a larger probability of appearing on the right than on the left. Because the cues were predictive, it is not possible to decide whether the perceptual benefits were due to automatic or voluntary processes. We reexamined this question by systematically varying the predictability of the cue. We found that perceptual performance was only improved if the cue was predictive. In contrast, reaction times showed effects of cueing regardless of whether the cues were predictive or not. In a further experiment, we used the gaze direction of a face presented at fixation as a cue (eyes looking right or left). Compared to flashes, gaze direction produced very similar results on perceptual performance. However, cueing benefits on reaction time were absent with gaze cues.
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