Introduces a linear regression method for investigating unconscious cognition. For words that were obscured by simultaneous dichoptic masking, indirect effects (semantic priming) and direct effects (perceptual identification) were assessed in 20 experiments (total N = 2,026). When measures of both indirect and direct effects have rational zero points, a statistically significant intercept in the indirect-on-direct-measure regression shows that (a) the indirect effect occurred in the absence of the direct effect, and (b) unconscious cognition is involved. For a position discrimination task, but not for an evaluative decision task, indirect-on-direct regression showed the significant intercept effect. Although small in magnitude, this intercept effect provides the statistically most secure finding yet obtained of a much-sought and controversial data pattern-indirect effect with no direct effect. With one added assumption (which appears plausible for the present data), this pattern indicates that unconscious cognition is dissociated from (i.e., occurs separately from) conscious cognition. In the last decade there has been a dramatic increase in the acceptability of theoretical interpretations of research find-ings in terms of unconscious cognition. Part of the shift is

& Using transcranial magnetic stimulation (TMS), we have tested the time needed for the perceived onset of spontaneous motor intention to be fully determined. We found that TMS applied over the presupplementary motor area after the execution of a simple spontaneous action shifted the perceived onset of the motor intention backward in time, and shifted the perceived time of action execution forward in time. The size of the effect was similar regardless of whether TMS was applied immediately after the action or 200 msec after. The results of three control studies suggest that this effect is timelimited, specific to modality, and also specific to the anatomical site of stimulation. We conclude that the perceived onset of intention depends, at least in part, on neural activity that takes place after the execution of action. A model, which is based on the mechanism of cue integration under the presence of noise, is offered to explain the results. The implications for the conscious control of spontaneous actions are discussed. &

We report three experiments investigating the effect of perceptual grouping on the appearance of a bistable apparent-motion (Ternus) display. Subjects viewed a Ternus display embedded in an array of context elements that could potentially group with the Ternus elements. In contrast to several previous findings, we found that grouping influenced apparent motion perception. In Experiment 1, apparent motion perception was significantly affected via grouping by shape similarity, even when the visible persistence of the elements was controlled. In Experiment 2, elements perceived as moving without context were perceived as stationary when grouped with stationary context elements. In Experiment 3, elements perceived as stationary without context were perceived as moving when grouped with moving context elements. We argue that grouping in the spatial and temporal domains interact to yield perceptual experience of apparent-motion displays. As we move through the three-dimensional world, the image formed at the retina is fragmented in space and time due to occlusion. For example, a coffee cup may partly occlude a book lying on the table behind it, producing spatial fragmentation of the book; or a chair may temporarily be occluded by a table as an observer walks by, producing fragmentation in time of the chair. However, perceptual experience is coherent and continuous in space and time. A major goal of perceptual theorists has been to explicate the principles and mechanisms of perceptual organization that give rise to perceptual coherence despite the fragmentary nature of the retinal image. This effort began with the Gestalt psychologists 80 years ago (e.g., Koffka,

We examined the time course of threshold reduction in the Gabor lateral masking paradigm (Polat and Sagi 1993). Contrast detection thresholds were measured (2AFC) for a briefly presented (36 msec) foveal Gabor signal (GS), preceded by a presentation (90 msec) of two high-contrast GS flanked masks, with Stimulus Onset Asynchrony (SOA) varying from 0 to 16,290 msec. Using target-to-mask separations of 3 and 12 (=0.15 ffi , GS wavelength), the 3 separated GS masks enhanced target threshold by 0.25 log units at SOA=0 and by 0.17 log units at 2,700 msec. At 12 separation, threshold was enhanced by 0.11 log units at SOA=0 and by 0.14 log units at 2,700 msec. Long-range (12) and short-range (3) enhancements persisted for over 16 seconds. Delayed and simultaneous enhancement depended on the stimulus configuration (maximal for collinear target and masks), local parameters (orientation, spatial frequency, and phase), and the presented eye (dichoptic vs. monoptic). The results suggest that spat...

or their technical expertise. Correspondence concerning this article should be addressed to John M. Henderson, Department of Psychology, Michigan State University, East Lansing, Michigan, 48824-1117. Electronic mail may be sent to john@eyelab.msu.edu. bject perception is a dynamic process: The entire visual scene disappears and then reappears three to four times each second during saccadic eye movements. How does the human visual system integrate this continually changing input? The purpose of the present study was to investigate the nature of the representational systems that support the retention and integration of information about real-world objects across saccades during dynamic visual perception. One intuitively appealing hypothesis concerning transsaccadic integration is that detailed sensory representations are created and fused from one fixation to the next within a spatiotopically organized reference frame (e.g., Breitmeyer, 1984; Davidson, Fox, & Dick, 1973;

& In visual backward masking, the visibility of a briefly presented visual target is disrupted by a mask that is presented shortly thereafter. The goal of the current study was to identify regions in the human cortex that may provide the neural basis of visual masking. We searched for areas whose activity correlated with perception as we systematically varied the strength of masking. A total of 13 subjects performed a backward masking task during functional magnetic resonance imaging. Target and mask were presented at three delay intervals (34, 68, and 102 msec) and behavioral measures confirmed that the targets were more visible at longer masking intervals. Two sets of regions of interest were identified: Distinct regions in the visual cortex (V1/V2, LO, hMT+) were segregated using scans to localize visual processing drawn from the existing literature. Additional cortical regions were selected in a data-driven approach based on their activity during the backward masking task. For each set, we determined the regions whose magnitude of activation increased at longer masking intervals. Nine of the subjects provided valid behavioral performance data on the visual masking task and imaging data from these subjects were used for subsequent analysis. The

When two successive stimuli are presented within 0 to 200ms intervals, the recognition of the first stimulus (the target) can be impaired by the second (the mask). This backward masking phenomenon has a form called metacontrast masking where the target and the mask are in close spatial proximity but not overlapping. In that case, the masking effect is strongest for interval of 60-100ms. To understand this behaviour, activity propagation in a feedforward network of leaky integrate-and fire neurons is investigated. It is found that, if neurons have a selectivity similar to that of V1 simple cells, activity decays layer after layer and ceases to propagate. To combat this, a local amplification mechanism is included in the model, using excitatory lateral connections, which turn out to support prolonged self-sustained activity. Masking is assumed to arise from local competition between representations recruited by the target and the mask. This tends to interrupt sustained firing, while prolonged retinal input tends to re-initiate it. Thus, masking causes a maximal reduction of the duration of the cortical response to the target towards the end of the retinal response. This duration exhibits the typical U-shape of the masking curve. In this model, masking does not alter the propagation of the onset of the response to the target, thus preserving response reaction times and enabling unconscious priming phenomena.

extent of crowding in peripheral vision does not scale

Periventricular white matter damage affecting large bundles connecting distant cortical areas may constitute the main neuronal mechanism for the deficit of controlled information processing observed in patients with early multiple sclerosis (MS). Visual backward masking has been demonstrated to affect late stages of conscious perception involving long-range interactions between visual perceptual areas and higher level integrative cortices while leaving intact early feed-forward visual processing and even complex processing such as object recognition or semantic processing. We therefore hypothesized that patients with early MS would have an elevated masking threshold, because of an impairment of conscious perception whereas subliminal processing of masked stimuli would be preserved. Twenty-two patients with early MS and 22 normal controls performed two backward-masking experiments. We used Arabic digits as stimuli and varied quasi-continuously the temporal interval with a subsequent mask, thus allowing us to progressively “unmask ” the stimuli. We finely quantified the visibility of the masked stimuli using both objective and subjective measures, thus obtaining accurate estimates of the threshold duration for access to consciousness. We also studied the priming effect caused by the variably masked numbers on a comparison task performed on a subsequently presented and highly visible target number. The threshold for access to consciousness of masked stimuli was elevated in MS patients compared to controls, whereas non-conscious processing

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