Is perception discrete or continuous?

How does conscious perception evolve following stimulus presentation? The idea that perception relies on discrete processing epochs has been often considered, but never widely accepted. The alternative, a continuous translation of the external world into explicit perception, although more intuitive and subjectively appealing, cannot satisfactorily account for a large body of psychophysical data. Cortical and thalamocortical oscillations in different frequency bands could provide a neuronal basis for such discrete processes, but are rarely analyzed in this context. This article reconciles the unduly abandoned topic of discrete perception with current views and advances in neuroscience.     

They Might as Well be in Bolivia: Race,Ethnicity and the Problem of Solid Organ Donation

Theoretical Medicine and Bioethics -     

Distanced Perspectives: Aids,Anencephaly, and Ahp

US court decisions guaranteeing life-sustaining care to anencephalic infants have been viewed with disfavor, and sometimes disbelief, by some ethicists who do not believe in the necessity of life-sustaining support for those without cognitive abilities or an independently sustainable future. The distance between these two views – one legal and inclusive, the other medical and specific – seems unbridgeable. This paper reports on a program using multicriterion decision making to define and describe persons in a way which both acknowledges the differences perceived by many as well as those commonalities insisted on in U.S. court decisions. It does this through application of the Analytic Hierarchy Process to a hierarchy of humanness criteria, and secondarily through reference to that concept's subset, personhood.     

Recall and recognition processes in motor memory: effects of feedback and knowledge of results delay

In linear movement tasks of 200 msec (Experiment 1 -ballistic movement) and 500 msec (Experiment 2 - nonballistic movement), motor recall strength was assessed by absolute, constant, and variable error; recognition strength was assessed by Z'-transformed actual-estimate correlations and absolute actual-estimate difference scores. Contrary to predictions, neither increased KR delay (45 vs. 5 sec) nor limited visual-auditory-tactile feedback caused decrements in recognition processes over KR-training or KR-withdrawal trial blocks for the 200-msec task. In the 500-msec task, the independent variables impaired recognition through training and transfer trials but impaired recall only in the training trials. Results generally did not support the hypothesized independence between recall and recognition processes. Several methodological issues related to recall, and recognition research were discussed.     

Influences of closure,occlusion, and size on the perception of fragmented pictures

Two experiments examined the ability to recognize a repeated figure in stimuli where only fragments of the figures were presented. Fragments were either closed or open regions presented either with or without an occluder that filled the spaces between the fragments (Experiment 1). Recognition performance was significantly better for open fragments, with or without an occluder, contrary to previous assertions that the occluder is the important factor for recognition. When stimulus size was varied, an occluder hindered recognition performance in the smallest size condition relative to unoccluded stimuli, which were equally easy to recognize across all size conditions (Experiment 2). The size results support the idea of size invariance in object naming. The difficulty in the smallest occluded condition is discussed in terms of differences in global and local processing depending on visual angle and sparsity     

Verbal response-effect compatibility

Ideomotor theory states that motor responses are activated by an anticipation of their sensory effects. We assumed that anticipated effects would produce response-effect (R-E) compatibility when there is dimensional overlap of effects and responses. In a four-choice task, visual digit stimuli called for verbal responses (color names). Each response produced a written response-effect on the screen. In different groups, the response-effect was a colored color word (e.g., blue in blue), a white color word, or a colored nonword (Xs in blue). In different blocks, the predictable effects were either incompatible (e.g., response "blue" --> effect: green) or compatible with the response. We found faster responses with compatible than with incompatible R-E mappings. The compatibility effect was strongest with colored words, intermediate with white words, and smallest with colored nonwords. We conclude that effect anticipation influences response selection on both a perceptual level (related to the word's color) and a conceptual level (related to the word's meaning).     

The influence of overlapping response sets on task inhibition

The aim of the present study was to examine the contribution of overlapping response sets to the occurrence of task inhibition, measured as n-2 task repetition cost. We had subjects switch among four tasks. Three tasks overlapped on both stimulus set and response set. A fourth, neutral, univalent task never overlapped on the stimulus set but, across three experiments, varied in terms of the degree of overlap in the response set. We found that overlap in response set affects task inhibition. We suggest that response set overlap increases the competition among tasks and, thus, triggers task inhibition to resolve this competition.     

Orthogonal cross-task compatibility: Abstract spatial coding in dual tasks

Spatially orthogonal stimulus and response sets can produce compatibility effects. To explore whether such effects cross the border of logically independent tasks, we combined a nonspeeded visual task requiring verbal report of a stimulus movement (up vs. down) with an auditory reaction time task that required a unimanual movement to the left or right. Two experiments demonstrated that up stimuli facilitate rightward responses and down stimuli facilitate leftward responses, relative to the opposite combinations, thus producing an orthogonal cross-task compatibility effect. This effect presumably arises from abstract coding with respect to the salient referents of a spatial dimension (i.e., up and right), so that coactivation of structurally similar codes leads to mutual priming even when the codes refer to different tasks. The present evidence for abstract spatial coding extends previously proposed coding principles from single-task settings to dual-task settings.     

Cue type affects preparatory influences on task inhibition

The present study investigates the influence of preparation on inhibitory effects in cued task switching. In three experiments, we assessed n − 2 repetition costs as marker of inhibition of the just executed and now irrelevant task by comparing performance in task sequences such as ABA (i.e., n − 2 repetitions, with A, B and C standing for different tasks) to task sequences such as CBA (i.e., n − 2 switches). Specifically, we varied the cue–target interval (CTI) to examine cue-based preparation effects. In addition, we manipulated cue type (i.e., abstract, verbal, and direct cues) across the three experiments. We obtained significant reductions of n − 2 repetition costs with prolonged CTI when using abstract cues (i.e., coloured frames) and task names (i.e., digit), but not when using the task-specific stimulus–response mapping as cue for the upcoming task. These data suggest that cue-based preparation is not a uniform process but depends on the information provided by the cue.