Perceptual grouping in visual word recognition

Morphine has been reported to possess immunosuppressive actions in both in vitro as well as in vivo assays of immune function. Our work in female B6C3F1 mice, surgically implanted with a 75-mg time release morphine pellet, has confirmed previous reports of a rapid loss in the cellularity of the spleen and thymus. To evaluate the effect of morphine on the subpopulations of cells in the thymus, two color fluorescence flow cytometry studies were performed. Fluorescently conjugated monoclonal antibodies specific for the murine cell surface CD4 and CD8 markers were used to identify the four major subpopulations of thymocytes. These studies indicated that morphine pellet-implanted mice suffered a loss in each of the four thymocyte subpopulations in comparison to placebo-implanted mice. However, the loss (> 90%) in the important CD4+/CD8+ subpopulation of immature thymocytes greatly exceeded that which was observed for any other subpopulation. Kinetic studies of morphine's effect on the thymocyte subpopulations revealed that the maximal depletion of the CD4+/CD8+ cells occurs approximately 4 days after pellet implantation. Thymocyte cell populations recovered by 14 days, with an increase above placebo for the double positive cells. Naltrexone administration blocked thymic alterations, suggesting that these immunologic consequences of morphine may be mediated through an opiate receptor. Measurements in thymocytes from morphine pellet-implanted mice showed an increased level of DNA fragmentation, whereas in vitro exposure to morphine (1-100 microM) produced no such increases. This suggests morphine may be working indirectly to induce apoptosis of immature thymocytes.     

Perceptual load influences selective attention across development.

Research suggests that visual selective attention develops across childhood. However, there is relatively little understanding of the neurological changes that accompany this development, particularly in the context of adult theories of selective attention, such as N. Lavie's (1995) perceptual load theory of attention. This study examined visual selective attention across development from 7 years of age to adulthood. Specifically, the author examined if changes in processing as a function of selective attention are similarly influenced by perceptual load across development. Participants were asked to complete a task at either low or high perceptual load while processing of an unattended probe stimulus was examined using event related potentials. Similar to adults, children and teens showed reduced processing of the unattended stimulus as perceptual load increased at the P1 visual component. However, although there were no qualitative differences in changes in processing, there were quantitative differences, with shorter P1 latencies in teens and adults compared with children, suggesting increases in the speed of processing across development. In addition, younger children did not need as high a perceptual load to achieve the same difference in performance between low and high perceptual load as adults. Thus, this study demonstrates that although there are developmental changes in visual selective attention, the mechanisms by which visual selective attention is achieved in children may share similarities with adults. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Feature-specific effects of selective visual attention

Four experiments were conducted to quantify the effect of performing a foveal discrimination task on sensitivity for a peripheral grating. The observer's primary task was to discriminate either the spatial frequency or orientation of successive foveal Gabor patches. On a third of the trials they also performed a secondary task to detect the presence of a near-threshold grating in the periphery. We find that sensitivity for detection of the peripheral grating depends on the similarity of the spatial frequencies and orientations between the foveal and peripheral stimuli. Importantly, sensitivity is also affected by which feature is being discriminated in the central task. Because the detectability of the peripheral grating is different when different features of the central stimuli are discriminated, we suggest that the effects on sensitivity are due to feature-specific attention and not simply to passive interactions between filters with similar tuning properties.     

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)     

Probability matching in visual selective attention.

J. Jonides (see record 1981-22746-001) suggested a model to account for shifts of spatial attention in visual search tasks with less than 100% cue validity. This 2-stage probability matching model was subsequently tested by Jonides (see record 1984-08558-001). Reaction time (RT) distribution characteristics provided some support for the model. The present author reanalyzes Jonides's data (including that published in 1981). Analysis showed strong support for the probability matching hypothesis. It is concluded that probability matching is an important strategic characteristic of visual spatial attention. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of selective attention during visual search.

Monitored eye movements in 8 2nd graders, 8 6th graders, and 8 college students during a search task in which Ss were given different types of information about target location before trial onset. Whereas color cues facilitated search performance in the 2 older groups, form cues were less successful in facilitating search and significantly interfered with search relative to a control condition for the 2nd graders. Both facilitation and interference effects in overall search times were related to number of fixations rather than to average fixation during a trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual grouping by infants and preschool children.

We tested infants 6 to 8 months and children 5? years of age for their discrimination of silent intervals between elements of auditory patterns. Standard patterns consisted of six 200-ms tones, three at 440 Hz and three at 659 Hz, with 200-ms intertone intervals (XXXOOO). Contrasting patterns differed only in the addition of a silent increment following the third tone (i.e., between tone groups, XXXOOO) or following the fourth tone (i.e., within a tone group, XXXOOO). Contrasting stimuli presented to infants had increments of 200, 125, 100, or 75 ms; those presented to children had increments of 100, 75, and 50 ms. Infants detected all increments in all locations except the 75-ms increment in the between-group location, but there were no differences in performance for different increment locations. Children detected all increments, but performed significantly worse for between-group increments than for within-group increments. Thus, the context of a temporal increment influences its detectability for children, as it does for adults, indicating that children group the elements of auditory stimuli on the basis of frequency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of hypertension and age in visual selective attention performance.

Previous research suggests that some aspects of cognitive performance decline as a joint function of age and hypertension. In this experiment, 51 unmedicated individuals with mild essential hypertension and 48 normative individuals, 18–78 yrs of age, performed a visual search task. The estimated time required to identify a display character and shift attention between display positions increased with age. This attention shift time did not differ significantly between hypertensive and normotensive participants, but regression analyses indicated some mediation of the age effect by blood pressure. For individuals less than 60 yrs of age, the error rate was greater for hypertensive than for normotensive participants. Although the present design could detect effects of only moderate to large size, the results suggest that effects of hypertension may be more evident in a relatively general measure of performance (mean error rate) than in the speed of shifting visual attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The stabilization of cortical evoked potentials during selective visual attention

The event-related potentials (ERP) to lateralized moving visual stimuli (administered to the right and to the left of the subject) were recorded in six derivations in eight healthy subjects during passive viewing and selective attention to one of the stimuli (the relevant one), which demanded precise and rapid motor reaction. It was shown that during the selective voluntary attention correlation between successive ERP was substantially higher than that under conditions of passive (involuntary) attention, i.e. the ERP in the occipital, parietal, and frontal derivations during voluntary attention were more stable. The less was correlation between the ERP at passive viewing, the greater was the difference between the values of correlation coefficients during selective and passive attention. It is suggested that role of selected attention consists in stabilization of activity of the cortical structures, which are involved in solving the behavioral task.     

Event-related potentials during visual selective attention in children of alcoholics

Event-related potentials were recorded from 7- to 18-year-old children of alcoholics (COAs, n = 50) and age- and sex-matched control children (n = 50) while they performed a visual selective attention task. The task was to attend selectively to stimuli with a specified color (red or blue) in an attempt to detect the occurrence of target stimuli. COAs manifested a smaller P3b amplitude to attended-target stimuli over the parietal and occipital scalp than did the controls. A more specific analysis indicated that both the attentional relevance and the target properties of the eliciting stimulus determined the observed P3b amplitude differences between COAs and controls. In contrast, no significant group differences were observed in attention-related earlier occurring event-related potential components, referred to as frontal selection positivity, selection negativity, and N2b. These results represent neurophysiological evidence that COAs suffer from deficits at a late (semantic) level of visual selective information processing that are unlikely a consequence of deficits at earlier (sensory) levels of selective processing. The findings support the notion that a reduced visual P3b amplitude in COAs represents a high-level processing dysfunction indicating their increased vulnerability to alcoholism.     

Abrupt visual onsets and selective attention: Voluntary versus automatic allocation.

The hypothesis that abrupt visual onsets capture attention automatically, as suggested by S. Yantis and J. Jonides (see record 1985-19225-001), was tested in four experiments. A centrally located cue directed attention to one of several stimulus positions in preparation for the identification of a target letter embedded in an array of distractor letters. In all experiments, one stimulus (either the target or one of the distractors) had an abrupt onset; the remaining letters did not. The effectiveness of the cue was manipulated (varying either its duration or its predictive validity) to test whether abrupt onsets capture attention even when subjects are in a highly focused attentional state. Results showed that onsets do not necessarily capture attention in violation of an observer's intentions. A mechanism for partially automatic attentional capture by abrupt onset is proposed, and the diagnosticity of the intentionality criterion for automaticity is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of age and task demands on visual selective attention.

We investigated whether young and older adults differ on measures of interference (INT), negative priming (NP), and inhibition of return (IOR) on a spatial selective attention task that gradually increased in cognitive demand, from simple perceptual matching to letter identification. For both groups, INT increased and IOR decreased with task demand; while NP remained stable. We found age-related increases in INT, NP, and IOR, independent of task demand. However, only between-groups differences in IOR remained after correcting for age-related slowing in response times. Finally, we found no association between our measures of attention across groups, suggesting negligible overlap between INT, NP, and IOR. Our results indicate that attention is selectively and independently influenced by age and task demands, with both effects dependent on how attention is measured. These findings shed light on the “frontal hypothesis of aging.” (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experience-dependent perceptual grouping and object-based attention.

Earlier studies have shown that attention can be directed to objects, defined on the basis of generic grouping principles, highly familiar shapes, or task instructions, rather than to contiguous regions of the visual field. The 4 experiments presented in this article extend these findings, showing that object attention benefits--shorter reaction times to features appearing on a single object--apply to recently viewed novel shapes. One experiment shows that object attention operates even when the visible fragments correspond to objects that violate standard completion heuristics. Other experiments show that experience-dependent object benefits can apply to fragments even without evidence of occlusion. These results attest to the flexible operation of the perceptual system, adapting as a function of experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age-related changes in selective attention and perceptual load during visual search.

Three visual search experiments were conducted to test the hypothesis that age differences in selective attention vary as a function of perceptual load (E. A. Maylor & N. Lavie, 1998). Under resource-limited conditions (Experiments 1 and 2), the distraction from irrelevant display items generally decreased as display size (perceptual load) increased. This perceptual load effect was similar for younger and older adults, contrary to the findings of Maylor and Lavie. Distraction at low perceptual loads appeared to reflect both general and specific inhibitory mechanisms. Under more data-limited conditions (Experiment 3), an age-related decline in selective attention was evident, but the age difference was not attributable to capacity limitations as predicted by the perceptual load theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual depth synthesis in the visual system as revealed by selective adaptation.

Selective adaptation was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual grouping affects pitch judgments across time and frequency.

Pitch, the perceptual correlate of fundamental frequency (F0), plays an important role in speech, music, and animal vocalizations. Changes in F0 over time help define musical melodies and speech prosody, while comparisons of simultaneous F0 are important for musical harmony, and for segregating competing sound sources. This study compared listeners' ability to detect differences in F0 between pairs of sequential or simultaneous tones that were filtered into separate, nonoverlapping spectral regions. The timbre differences induced by filtering led to poor F0 discrimination in the sequential, but not the simultaneous, conditions. Temporal overlap of the two tones was not sufficient to produce good performance; instead performance appeared to depend on the two tones being integrated into the same perceptual object. The results confirm the difficulty of comparing the pitches of sequential sounds with different timbres and suggest that, for simultaneous sounds, pitch differences may be detected through a decrease in perceptual fusion rather than an explicit coding and comparison of the underlying F0s. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual grouping and spatial distortion: A developmental study.

20 Ss in each of 5 age groups (kindergartners; 2nd, 4th, and 6th graders; and graduate students) estimated distances between elements in patterns illustrating the Gestalt grouping principles of proximity, similarity, closure, and good continuation. Ss of all age groups consistently judged distances between elements in the same perceptual group as smaller than physically identical distances between elements in different perceptual groups, which indicated that all Ss were sensitive to the structure of the Gestalt patterns. The magnitude of these distance distortions decreased significantly with age, which suggests that perceptual development includes improvements in the ability to disregard Gestalt groupings when the task requires selective attention to certain elements. Results are consistent with evidence that perceptual development moves from visual processing based primarily on global attributes of patterns to processing that can selectively analyze the component structure of patterns. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual grouping due to pitch and amplitude in hallucinating schizophrenics

Acquired deficiencies of fibrinogen, antithrombin III and plasminogen are reported in liver disease, and it is known that their plasma levels fluctuate during the day. The aim of this study was to investigate the circadian rhythms of these three factors in chronic liver disease. Five groups of subjects were considered: (A) 15 healthy controls: (B) 15 patients with hepatic alcoholic steatosis; (C) 15 patients with chronic active hepatitis; (D) 15 patients with compensated cirrhosis of the liver, and (E) 15 patients with decompensated cirrhosis with ascites. The levels of fibrinogen, antithrombin III and plasminogen were determined in blood samples drawn in each subject during the span of a day every 3 h starting from midnight. The time-related values were analyzed using the 'population-mean cosinor' method. Groups A and B presented a significant (p < 0.05) circadian rhythm for each variable, group C a significant (p < 0.05) circadian rhythm for fibrinogen and antithrombin III and groups D and E no significant (p > 0.05) circadian rhythms. Statistically significant differences (p < 0.05) were demonstrated among the groups in the mean daily levels of the three variables by ANOVA, the concentrations decreasing with disease severity. These data confirm the existence of a significant diurnal periodicity in the circulating levels of fibrinogen, antithrombin III and plasminogen in controls and suggest that liver disease is associated with progressive circadian modifications in the temporal structure of fibrinogen, antithrombin III and plasminogen, related to the stage of the liver disease. The rhythm derangements may be considered markers of evolution in liver disease.     

Perceptual load modulates object-based attention.

Two experimental series are reported using both reaction time (RT) and a data-limited perceptual report to examine the effects of perceptual load on object-based attention. Perceptual load was manipulated across 3 levels by increasing the complexity of perceptual judgments. Data from the RT-based experiments showed object-based effects when the target was near the cued location. Results from the data-limited procedure showed that, with low perceptual load, attention spread along the cued object, supporting an object-based attention account. As load increased, attention was constrained to object locations near the cue, but attention still favored the cued object, inconsistent with a scanning prioritization account of object-based attention effects. Furthermore, findings showed that perceptual load modulates object selection in a manner similar to spatial attention, suggesting that there might be a common process underlying object-based and spatial attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)