Converging operations for perceptual defense.

Discusses some recent experimental attempts to provide converging operations for a concept of perceptual defense. For present purposes, perceptual defense is defined as a relative failure of perception per se due to the emotional character of the stimulus. Experiments are evaluated and discussed mainly in terms of their ability to eliminate as an explanation the response-bias hypothesis for differential accuracy between neutral and emotional words. In addition, following Blum, a stimulus-effect hypothesis is described and applied; all the experiments discussed require, if differences in accuracy of recognition are to be attributed to perceptual variation, converging operations to eliminate this hypothesis. It is argued as well that the search for converging operations for perceptual defense has implications for methodology in other areas of perception. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric asymmetries for global and local visual perception: Effects of stimulus and task factors.

Although neurological and physiological studies indicate a right hemisphere superiority in global processing and a left hemisphere superiority in local processing of Navon-type hierarchical letters (D. Navon, 1977), most investigations of lateralized perception in healthy participants report neither asymmetry. In 6 experiments the authors examined the influence of attentional demands, stimulus properties, and mode of response on perceptual asymmetries for global and local perception. Consistent with their theoretical predictions, asymmetries were more robust on divided- than focused-attention tasks and in response to stimuli in which local and global levels were equally salient compared with those with greater global than local saliency. Contrary to their prediction, perceptual asymmetries were not influenced by the complexity of the motor response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Primacy of dimensions in color perception.

Used a procedure called selective/individual rotation to investigate the role of dimensions in the perception of color. Ss performed either selective-attention or divided-attention tasks to paired dimensions created from each of 3 orientations of axes in color space: 0°, 22.5°, and 45°. The authors evaluated a Euclidean hypothesis, namely, that speeded classification of interacting dimensions is invariant to rigid rotation of stimulus axes. All experiments obtained evidence against this Euclidean hypothesis. Exps 1–4 showed that selective attention was best at the orientation corresponding to saturation and brightness, suggesting primacy of these dimensions. The results were replicated with the pairs hue–saturation (Exp 7) and hue–brightness (Exp 8). The authors conclude that interacting dimensions can be primary and that dimensional primacy characterizes much of perceptual experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional sensitization of unconscious cognition: Task sets modulate subsequent masked semantic priming.

According to classical theories, automatic processes are autonomous and independent of higher level cognitive influence. In contrast, the authors propose that automatic processing depends on attentional sensitization of task-congruent processing pathways. In 3 experiments, the authors tested this hypothesis with a modified masked semantic priming paradigm during a lexical decision task by measuring event-related potentials (ERPs): Before masked prime presentation, participants attended an induction task either to semantic or perceptual stimulus features designed to activate a semantic or perceptual task set, respectively. Semantic priming effects on the N400 ERP component, an electrophysiological index of semantic processing, were obtained when a semantic task set was induced immediately before subliminal prime presentation, whereas a previously induced perceptual task set attenuated N400 priming. Across experiments, comparable results were obtained regardless of the difficulty level and the verbal or nonverbal nature of the induction tasks. In line with the proposed attentional sensitization model, unconscious semantic processing is enhanced by a semantic and attenuated by a perceptual task set. Hence, automatic processing of unconscious stimuli is susceptible to top-down control for optimizing goal-related information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention allocation modulates the processing of hierarchical visual patterns: A comparative analysis of capuchin monkeys (Cebus apella) and humans.

Humans show a global advantage when processing hierarchical visual patterns, and they detect the global level of stimulus structure more accurately and faster than the local level in several stimulus contexts. By contrast, capuchins (Cebus apella) and other monkey species show a strong local advantage. A key factor which, if manipulated, could cause an inversion of this effect in monkeys is still to be found. In this study, we examined whether it was possible to induce attention allocation to global and local levels of perceptual analysis in capuchin monkeys and if by doing so, their local dominance could be reversed. We manipulated attentional bias using a matching-to-sample (MTS) task where the proportion of trials requiring global and local processing varied between conditions. The monkeys were compared with humans tested with the same paradigm. Monkeys showed a local advantage in the local bias condition but a global advantage in the global bias condition. The role of attention in processing was confined to the local trials in a first phase of testing but extended to both local and global trials in the course of task practice. Humans exhibited an overall global dominance and an effect of attentional bias on the speed of processing of the global and local level of the stimuli. These results indicate a role for attention in the processing of hierarchical stimuli in monkeys and are discussed in relation to the extent to which they can explain the differences between capuchin monkeys and humans observed in this and other studies. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The myth of perceptual defect: Sources and evidence.

A hypothesis of a perceptual defect in Black populations, suggested tentatively 20 yrs ago by L. E. Tyler (1956), was found to be still prevalent in the research literature. The hypothesis, its original data base, and more recent literature are examined. It was found that the hypothesis did not distinguish between the effects of race vs early experience on perceptual functioning. Reflecting this confusion, the authors argue that the original data base for the hypothesis was seriously flawed. Many studies assumed that the hypothesis could be demonstrated by lower scores on performance than on verbal subtests of IQ test batteries. The inadequacy of this assumption is discussed, and the use of IQ subtests to assess perceptual functioning is criticized. The need for measurement of response biases when attempting to assess group differences in perception is also stressed. An examination of the literature found few direct tests of ethnic differences in perception. Although some data tentatively suggest that there may be differences in visualization of spatial transformations, similar to the differences that have been found between the sexes, it is concluded that not enough data are available to make any general statement about ethnic differences in perception. (21/4 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reading ability and semantic processing: Isolating speed of access.

Although much attention has focused on the efficiency of access to semantic information as a determinant of reading ability, previous research has confounded information access and decision processes. The authors used a matching task to study the time course of semantic access among college students. They studied the time course of processing by varying the stimulus onset between the two members of a stimulus pair. Semantic encoding functions obtained from this paradigm were used to isolate semantic access from the decision component of the matching task. Regression analyses indicated that the often-obtained correlation between speed of semantic processing and measures of reading ability is based on unique contributions from both semantic access and decision processes. The results undermine the hypothesis that the efficiency of access to semantic codes is a relatively age-variant contributor to individual differences in reading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention to hierarchical level influences attentional selection of spatial scale.

Ample evidence suggests that global perception may involve low spatial frequency (LSF) processing and that local perception may involve high spatial frequency (HSF) processing (Shulman, Sullivan, Gish, & Sakoda, 1986; Shulman & Wilson, 1987; Robertson, 1996). It is debated whether SF selection is a low-level mechanism associating global and local information with absolute LSF and HSF content, or whether it is a higher level mechanism involving a selective process that defines the SF range in which global and local can then be relatively defined. The present study provides support for the latter claim by demonstrating that allocating attention to global or local levels of hierarchical displays biased selection of LSFs or HSFs, respectively, in subsequently presented compound gratings. This bias occurred despite a change in the response dimension (from letter identification in the hierarchical stimulus to orientation discrimination in the grating) and despite a difference in retinal location of the hierarchical stimuli and the grating stimulus. Moreover, the bias was determined by the relationship between the 2 SFs in the compound grating (i.e., their relative frequency) rather than the absolute SF values. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anxiety and perceptual structure: Individual differences in neuropsychological function.

Studied the cognitive performance of 24 high and 36 low trait anxious undergraduates under conditions of high and low situational stress, using tasks requiring greater contribution of the right or left hemisphere. In addition, a perceptual task was adapted from visual information processing research to assess Ss' global or analytic approaches to perception; if anxiety increased the left hemisphere's contribution to perception, anxious Ss might be expected to be more analytic and detail oriented. Results show no significant differences on left hemisphere tasks but a significant interaction of trait by state anxiety for right hemisphere tasks: Low trait Ss performed better and high trait Ss performed more poorly under situational stress. Trait anxiety showed a significant main effect on visual information processing strategy, low Ss tending to be more global and high Ss tending to process the stimulus analytically. Results support the utility of a neuropsychological model in describing the effects of emotion on perception. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual load as a necessary condition for selective attention.

The early and late selection debate may be resolved if perceptual load of relevant information determines the selective processing of irrelevant information. This hypothesis was tested in 3 studies; all used a variation of the response competition paradigm to measure irrelevant processing when load in the relevant processing was varied. Perceptual load was manipulated by relevant display set size or by different processing requirements for identical displays. These included the requirement to process conjunctions versus isolated features and the requirement to perform simple detection of a character's presence versus difficult identification of its size and position. Distractors' interference was found only under low-load conditions. Because the distractor was usually clearly distinct from the target, it is concluded that physical separation is not a sufficient condition for selective perception; overloading perception is also required. This allows a compromise between early and late selection views and resolves apparent discrepancies in previous work. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibition of return is not detected using illusory line motion

Inhibition of return (IOR) is the name that has been assigned to a response time (RT) delay to a stimulus presented at a recently stimulated spatial location. A commonly held explanation for the origins of IOR is that perceptual processing in inhibited and that this inhibition translates into slower RT. Three experiments with 10 subjects were used to directly test this perceptual explanation. The first two experiments assessed the level of perceptual facilitation present in the IOR paradigm using the frequency and latency of illusory line motion judgments. Contrary to the predictions of the perceptual view, the line motion and RT measures revealed only speeded processing at previously stimulated spatial locations. Experiment 3 required a simple detection response and used the same stimulus and timing parameters as those in Experiments 1 and 2. IOR was present, replicating the recent finding that judgments based on perceptual qualities of the stimulus do not demonstrate a RT delay, whereas simple detection tasks do show RT inhibition at previously stimulated locations. These findings are discussed in relation to a number of hypotheses about the origin of the RT delay.     

Geometric psychology generates the visual Gestalt.

Discusses an appropriate theoretical structure for the gestalt principles of visual form perception that is consistent with anatomical and neurophysiological knowledge and builds positively on it. It is suggested that much is known about the detailed psychophysics and physiology of mammalian visual systems, but there has been little study of the ways local processes in the visual system work cooperatively to produce the global phenomena of perception. The gestalt psychologists demonstrated perceptual organization but were hindered in their theorizing by the primitive knowledge at that time of how the brain operates and an inadequate model of cortical function. Recent discoveries in visual anatomy and physiology suggest that brain functions can be modeled in terms of one or more differentiable topological structures. Discussed are the visual manifold; holonomy, integrability, and visual contours; transversality and the principle of transverse control; interlude; and relation to the visual gestalt. It is concluded that (1) all the elements of a differential geometric structure can be identified within the primary visual processing system and (2) the major gestalt laws of perceptual organization follow naturally from the mathematical structure. (French abstract) (4 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latencies in fMRI time-series: effect of slice acquisition order and perception

In BOLD fMRI a detailed analysis of the MRI signal time course sometimes shows time differences between different activated regions. Some researchers have suggested that these latencies could be used to infer the temporal order of activation of these cortical regions. Several effects must be considered, however, before interpreting these latencies. The effect of a slice-dependent time shift (SDTS) with multi-slice acquisitions, for instance, may be important for regions located on different slices. After correction for this SDTS effect the time dispersion between activated regions is significantly decreased and the correlation between the MRI signal time course and the stimulation paradigm is improved. Another effect to consider is the latency which may exist between perception and stimulus presentation. It is shown that the control of perception can be achieved using a finger-spanning technique during the fMRI acquisition. The use of this perception profile rather than an arbitrary waveform derived from the paradigm proves to be a powerful alternative to fMRI data processing, especially with chemical senses studies, when return to baseline is not always correlated to stimulus suppression. This approach should also be relevant to other kinds of stimulation tasks, as a realistic way of monitoring the actual task performance, which may depend on attention, adaptation, fatigue or even variability of stimulus presentation.     

Mechanisms of imagery-perception interaction.

A number of different research findings have shown that mental imagery can affect the perceptual processing of stimuli. The present research was aimed at characterizing the representations and processes underlying imagery–perception interactions. In 4 experiments, Ss mentally projected images of letters into the visual field, and either detected or detected and localized point threshold stimuli that fell on or off the image. Stimuli falling on the image were detected more often than stimuli falling off the image, consistent with the hypothesis that the representations at the interface between imagery and perception have an array format. When the facilitation was analyzed in terms of signal detection theory, it was found to consist only of criterion lowering, and not of enhanced sensitivity. The local criterion-lowering effect of imaged letters was then compared with the effect of perceiving a letter and attending to a letter. Perceiving a letter had no discernible effect on stimulus detection, whereas attending to the letter caused the same local criterion lowering, without sensitivity changes, as imaging the letter. This is consistent with the claims of U. Neisser (1976) and others that imagery is an attentional state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Illusory concomitant motion in ambiguous stereograms: Evidence for nonstimulus contributions to perceptual organization.

Performed 3 experiments to test whether perceptual organization is cognitively or motivationally penetrable. In Exp I, 8 undergraduate and graduate students viewed a reversible stereogram while instructed to hold 1 depth organization. Responses about depth were recorded indirectly by recording responses about direction of the illusory concomitant motion that is perceptually coupled to depth in a stereogram. It is contended that, inasmuch as perceptually coupled variables covary without necessary stimulus covariation, a postperceptual locus for any intention effects they exhibit is unlikely. Results show that instruction influenced perceived depth to a degree influenced by stimulus bias. Exps II and III examined the possibility that instructed intention might influence perception indirectly by influencing eye movements. Eight graduate student viewers' vergence position was measured directly through responses about alignment of a vernier nonius fixation. Findings from Exp II indicate an interaction between hold instruction and stimulus bias. However, unlike Exp I, instructed responses were larger with the depth response than with the motion response. Results from Exp III reveal that differential instructions produced different responses about perceptual organization, but that they were not reliably accompanied by different vergence movements. Overall findings suggest that instructed intention may influence perceptual organization by influencing internal nonstimulus components to the perceptual process. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Single units and conscious vision

Figures that can be seen in more than one way are invaluable tools for the study of the neural basis of visual awareness, because such stimuli permit the dissociation of the neural responses that underlie what we perceive at any given time from those forming the sensory representation of a visual pattern. To study the former type of responses, monkeys were subjected to binocular rivalry, and the response of neurons in a number of different visual areas was studied while the animals reported their alternating percepts by pulling levers. Perception-related modulations of neural activity were found to occur to different extents in different cortical visual areas. The cells that were affected by suppression were almost exclusively binocular, and their proportion was found to increase in the higher processing stages of the visual system. The strongest correlations between neural activity and perception were observed in the visual areas of the temporal lobe. A strikingly large number of neurons in the early visual areas remained active during the perceptual suppression of the stimulus, a finding suggesting that conscious visual perception might be mediated by only a subset of the cells exhibiting stimulus selective responses. These physiological findings, together with a number of recent psychophysical studies, offer a new explanation of the phenomenon of binocular rivalry. Indeed, rivalry has long been considered to be closely linked with binocular fusion and stereopsis, and the sequences of dominance and suppression have been viewed as the result of competition between the two monocular channels. The physiological data presented here are incompatible with this interpretation. Rather than reflecting interocular competition, the rivalry is most probably between the two different central neural representations generated by the dichoptically presented stimuli. The mechanisms of rivalry are probably the same as, or very similar to, those underlying multistable perception in general, and further physiological studies might reveal much about the neural mechanisms of our perceptual organization.     

Electrophysiological evidence for a shared representational medium for visual images and visual percepts.

Systematic effects of imagery on visual signal detection performance have been used to argue that imagery and the perceptual processing of stimuli interact at some common locus of activity (Farah, 1985). However, such a result is neutral with respect to the question of whether the interaction occurs during modality-specific visual processing of the stimulus. If imagery affects stimulus processing at early, modality-specific stages of stimulus representation, this implies that the shared stimulus representations are visual, whereas if imagery affects stimulus processing only at later, amodal stages of stimulus representation, this implies that imagery involves more abstract, postvisual stimulus representations. To distinguish between these 2 possibilities, we repeated the earlier imagery-perception interaction experiment while recording event-related potentials (ERPs) to stimuli from 16 scalp electrodes. By observing the time course and scalp distribution of the effect of imagery on the ERP to stimuli, we can put constraints on the locus of the shared representations for imagery and perception. An effect of imagery was seen within 200 ms following stimulus presentation, at the latency of the 1st negative component of the visual ERP, localized at the occipital and posterior temporal regions of the scalp, that is, directly over visual cortex. This finding supports the claim that mental images interact with percepts in the visual system proper and hence that mental images are themselves visual representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Subliminal perception reaffirmed.

Reviews the book, Preconscious Processing by Norman Dixon (see 1981). Dixon provides a fairly extensive review of relevant literature and concludes that the research findings provide overwhelming support for the reality of preconscious perceptual processes. Extensive treatment is given to clinical applications and selective attention, two topics that were virtually ignored in the earlier volume. In addition, the arguments have been made more general. It is for these reasons that Dixon now prefers the more general concept, preconscious processing, rather than the more limited concept, subliminal perception. A preconscious process, according to Dixon, is any perceptual or memorial process for which there is no awareness or conscious experience. He argues that since the capacity of both the senses and long-term memory exceeds that of the limited capacity channel of conscious experience, entry into the limited capacity channel must be determined at a preconscious stage of processing. More importantly, Dixon also argues that the meaning of a stimulus is processed preconsciously and that even when the preconscious processing of meaning does not lead to conscious experience, the products of this processing may affect conscious perceptual or memorial processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Global and local processing in adult humans (Homo sapiens), 5-year-old children (Homo sapiens), and adult cotton-top tamarins (Saguinus oedipus).

This study compared adults (Homo sapiens), young children (Homo sapiens), and adult tamarins (Saguinus oedipus) while they discriminated global and local properties of stimuli. Subjects were trained to discriminate a circle made of circle elements from a square made of square elements and were tested with circles made of squares and squares made of circles. Adult humans showed a global bias in testing that was unaffected by the density of the elements in the stimuli. Children showed a global bias with dense displays but discriminated by both local and global properties with sparse displays. Adult tamarins' biases matched those of the children. The striking similarity between the perceptual processing of adult monkeys and humans diagnosed with autism and the difference between this and normatively developing human perception is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Invariance of perceptual spaces and perceptual separability of stimulus dimensions

This article reports an extension of a paradigm for studying processing of perceptual dimensions. The paradigm is the complete identification task with a feature-complete factorial design (FCFD) of stimuli providing data for multidimensional signal detection analyses. The extension uses blocks of trials with subsets of the FCFD stimulus set, allowing estimation of various d's for inferring perceptual separability (PS) of dimensions and for disambiguating stimulus configurations when PS fails. Results of 4 experiments found the following: PS of arc curvature and line orientation in a discrimination task (Experiment 1), increasing PS failure in detection of horizontal and vertical lines (Experiment 2a), 45 degrees and 135 degrees (Experiment 2b), and 50 degrees and 60 degrees oblique lines (Experiment 2c). In each experiment, corresponding d's remained equivalent across blocks with different stimulus subsets.