This thesis claims that metacontrast unmasking is influenced by attentional orienting towards the target location. This view is contrary to Breitmeyer, Rudd and Dunn (1981), who proposed that metacontrast unmasking is the product of inhibition of the primary mask's transient signal by the sustained signal of a secondary mask. A series of experiments demonstrate the thesis using a task in which observers discriminated the missing corner of a target diamond. Experiments 1 and 2 replicated metacontrast masking and unmasking, respectively, experiment 3 illustrated that contour proximity had no influences on unmasking, contrary to dual-channel inhibition theory. Experiments 4 and 5 indicated that metacontrast unmasking was influenced by spatial orienting. We propose an addition of attention to dual-channel theory as it is incomplete with regards to metacontrast unmasking.

This thesis claims that metacontrast unmasking is influenced by attentional orienting towards the target location. This view is contrary to Breitmeyer, Rudd and Dunn (1981), who proposed that metacontrast unmasking is the product of inhibition of the primary mask's transient signal by the sustained signal of a secondary mask. A series of experiments demonstrate the thesis using a task in which observers discriminated the missing corner of a target diamond. Experiments 1 and 2 replicated metacontrast masking and unmasking, respectively, experiment 3 illustrated that contour proximity had no influences on unmasking, contrary to dual-channel inhibition theory. Experiments 4 and 5 indicated that metacontrast unmasking was influenced by spatial orienting. We propose an addition of attention to dual-channel theory as it is incomplete with regards to metacontrast unmasking. / Arts, Faculty of / Psychology, Department of / Graduate

No description available.

Thesis (Ph. D.)--University of California, San Diego, 2003. / Vita. Includes bibliographical references (leaves 102-105).

The present investigation was designed to answer the question of whether or not schizophrenia spectrum members exhibit increased susceptibility to perceptual and conceptual backward masking effects when processing complex stimulus events. Introductory psychology students were screened through the use of the Minnesota Multiphasic Personality Inventory (MMPI) to obtain 3 groups of subjects having inflation-free, 4-9, and 2-7-8 profiles. Immediate memory for pictures was assessed as a function errors in all of the groups for both correct and incorrectof mask type (picture, pattern, and noise), luminance (high vs. low), and mask delay (0 vs. 300 ms). No significant differences were found between the groups in their ability to recognize a picture in the absence of a mask. The frequency of mask target trials was discovered to be nonsignificant. Analysis of subjects’ number of correct target identifications as a function of group, mask type, luminance level and delay of mask revealed significant main effects for luminance and for delay of mask. However, no factor involving the group variable reached statistical significance. / Department of Psychological Science

Discrimination thresholds were obtained during a delayed spatial frequency discrimination task. In Experiment 1, we found that presentation of a mask 3 s before onset of a reference Gabor patch caused selective interference in a subsequent discrimination task. However, a 10 s interval abolished this masking effect. In Experiment 2, the mask was associated with a second spatial frequency discrimination task so that a representation of the mask had to be coded into short-term perceptual memory. The presence of this second discrimination task now caused similar interference effects on the primary discrimination task at both the 3 s and 10 s ISI conditions. The different results from these two experiments are best explained by a two-step perceptual memory mechanism. The results also provide further insight into the conditions under which stimulus representations are shared between the perceptual and memory domains.

La théorie dominante suggérant une séparation entre une vision consciente pour la perception et une vision non consciente pour l'action au sein du système visuel fut particulièrement discutée au cours des dernières décennies. La thèse défendue ici se positionne dans le cadre d'une approche alternative reposant sur une évaluation conjointe des réponses motrice et perceptive en présence de stimuli au seuil perceptif. Les travaux réalisés dans ce contexte ont initialement porté sur les temps de réaction et ont contribué au développement d'un modèle psychophysique postulant que les réponses perceptives et motrices dépendraient d'un signal sensoriel unique mais de seuils de décision spécifiques. Les trois études réalisées au cours de cette thèse ont permis de tester ces propositions à partir de travaux portant sur le contrôle moteur manuel. Tout en confirmant une forte association entre les traitements visuels pour la perception et pour l'action, ces travaux ont permis de mettre en évidence un rôle important des conditions expérimentales (par exemple le contraste des stimuli et la présence ou non d'un masque visuel) dans les résultats obtenus. Les résultats se sont révélés compatibles avec les modèles neurophysiologiques du masquage visuel qui postulent que la réponse neurale à une stimulation visuelle est constituée d'une vague d'activation feedforward associée à la présence physique de la stimulation et de boucles de rétroaction liées à la perception consciente de celle-ci. Nos travaux ont également permis d'adapter au contrôle moteur manuel le modèle de décision à signal unique initialement développé dans le cadre des études portant sur les temps de réaction. / The dominant position of a separation between a conscious vision for perception and an unconscious vision for action within the visual system has been particularly discussed in the last decades. The present dissertation is to be placed in the context of an alternative approach consisting in evaluating jointly both perceptual and motor responses in the presence of near-treshold visual stimuli. Previous work within this framework, which have mainly concerned reaction times, have contributed to develop a psychophysical model in which perceptual and motor decision are taken relatively to the same single incoming signal but are based on different tresholds. The three studies conducting during this PhD aimed to testing these proposals in experiments involving manual motor control. While confirming the strong link between perceptual and motor processing within the visual system, the results obtained in these studies underlined the importance of experimental parameters such as the contrast of the stimuli and the presence of visual masks. These results are congruent with neurophysiological models of visual masking, which postulate that the neural response to a visual stimulus is composed of a transient feedforward sweep of activation related to the presence of as stimulus and recurrent feedback loops linked to the conscious perception of this stimulus. Our work also led to the adaptation to manual motor control of the single signal decisional model initially developed on the basis of reaction time studies.

No description available.

Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references (leaves 154-163).

Stimuli that cannot be perceived (i.e., that are subliminal) can still elicit neural responses in an observer, but can such stimuli influence behavior and higher-order cognition? Empirical evidence for such effects has periodically been accepted and rejected over the last six decades. Today, many psychologists seem to consider such effects well-established and recent studies have extended the power of subliminal processing to new limits. In this thesis, I examine whether this shift in zeitgeist is matched by a shift in evidential strength for the phenomenon. This thesis consists of three empirical studies involving more than 250 participants, a simulation study, and a quantitative review. The conclusion based on these efforts is that several methodological, statistical, and theoretical issues remain in studies of subliminal processing. These issues mean that claimed subliminal effects might be caused by occasional or weak percepts (given the experimenters’ own definitions of perception) and that it is still unclear what evidence there is for the cognitive processing of subliminal stimuli. New data are presented suggesting that even in conditions traditionally claimed as “subliminal”, occasional or weak percepts may in fact influence cognitive processing more strongly than do the physical stimuli, possibly leading to reversed priming effects. I also summarize and provide methodological, statistical, and theoretical recommendations that could benefit future research aspiring to provide solid evidence for subliminal cognitive processing. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 4: Manuscript.</p><p> </p>