Quantitative theories of metacontrast masking.

In metacontrast masking, the effect of a visual mask stimulus on the perceptual strength of a target stimulus varies with the stimulus-onset asynchrony (SOA) between them. As SOA increases, the target percept first becomes weaker, bottoms out at an intermediate SOA, and then increases for still larger SOAs. As a result, a plot of target percept strength against SOA produces a U-shaped masking curve. Theories have proposed special mechanisms to account for this curve, but new mathematical analyses indicate that it is a robust characteristic of a large class of neurally plausible systems. The author describes 3 quantitative methods of accounting for the U-shaped masking effect and analyzes previously published mathematical models of masking. The models produce the masking curve through mask blocking, whereby a strong internal representation of the target blocks the mask's effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the relation between metacontrast masking and suppression of visible persistence.

Does the introduction of additional contours in a display sequence (an operation known to reduce the strength of suppression in metacontrast) also reduce suppression of visible persistence? In three experiments, duration of visible persistence was estimated by a method in which successful performance depends on the temporal integration of a pattern whose elements are displayed in two successive frames. In this procedure, the arrival of the trailing frame is known to exert a suppressive influence on the visible persistence of the leading frame. Embedding the elements of the leading frame within additional contours (a line grid) reduced the degree of suppression exerted by the trailing frame. This did not occur when the grid was part of the trailing display. We conclude that suppression of visible persistence and metacontrast masking belong to the same class of events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition in human adults without masking.

Latent inhibition refers to attenuated responding to Cue X observed when the X-outcome pairings are preceded by X-alone presentations. It has proven difficult to obtain in human adults unless the preexposure (X-alone) presentations are embedded within a masking (i.e., distracting) task. The authors hypothesized that the difficulty in obtaining latent inhibition with unmasked tasks is related to the usual training procedures, in which the preexposure and conditioning experiences are separated by a set of instructions. Experiment 1 reports latent inhibition without masking in a task in which preexposure and conditioning occur without interruption. Experiments 2 and 3 demonstrate that this attenuation in responding to target Cue X does not pass a summation test for conditioned inhibition and is context specific, thereby confirming that it is latent inhibition. Experiments 3 and 4 confirm that introducing instructions between preexposure and conditioning disrupts latent inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactions of forward and simultaneous masking in intensity discrimination

Intensity coding mechanisms are explored in a paradigm involving both forward and simultaneous masking. For intensity discrimination of 1000-Hz pure tone in quiet, a near-miss to Weber's law is observed. However, as more stimulus components are added to this relatively simple experiment, interactions among components produce a more complex pattern of results. An intense forward masker, while not causing any threshold shift for the test tone, produces a nonmonotonic intensity discrimination function ["the midlevel hump," Zeng et al., Hearing Res. 55, 223-230 (1991)]. The midlevel hump can be removed by the presence of additional notched noise [Plack and Viemeister, J. Acoust. Soc. Am. 92, 1902-1910 (1992)] or narrow-band noise whose level is increased along with the test tone's standard level. The same midlevel hump can also be enhanced by a fixed-low-level notched noise or a high-level, high-pass noise which causes minimal masking at the test frequency. Interactions of forward masking and simultaneous masking present a serious problem for a clear interpretation of these results. For example, the notched noise was originally intended to restrict off-frequency listening, but on-frequency masking compromised this original purpose and confounded the interpretation of the notched noise effects. By measuring systematically the growth-of-masking functions, the present study identified various interactions of forward and simultaneous masking and clarified the role of off-frequency listening in forward-masked intensity discrimination. Both peripheral and central mechanisms may have contributed to the occurrence, reduction and enhancement of the midlevel hump under these masking conditions.     

Cognition without awareness: Subliminal influences upon conscious thought.

A method was developed to record the impact of a subliminal registration upon the nature, extent, and quality of a S's conscious impressions of a perceived stimulus. The main questions raised were: (a) will impressions of a pictured person of ambiguous sex be affected by subliminal sexual drawings, and (b) will impressions of pictured person be differently affected by realistic and by symbolic subliminal sexual pictures? A balanced design was employed with 24 male medical students as Ss. It was found that Ss tended either to incorporate or exclude attributes of the subliminal sexual picture in their impressions of the perceived figure. Additional findings are discussed. 25 references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Texture discrimination with and without abrupt texture gradients.

Assessed whether effortless, visual texture discrimination relies on the detection of gradients between 2 textures in 2 experiments using a total of 32 undergraduates with manipulations that smoothed (Exp 1) or interrupted (Exp 2) the gradient between textures comprising L- and X-type micropatterns. Compared to discrimination performance when there was an abrupt discontinuity between juxtaposed textures, performance declined moderately (about 10%) when the texture boundary was smoothed. Abrupt texture gradients are not a necessary condition for the asymmetrical discrimination of 2 textures. Results indicate that, in certain instances, texture discrimination may involve pattern classification-like processes that are operative in the absence of texture gradients. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Backward pattern masking can vary as a nonmonotonic function of target duration: on the influence of intratraget metacontrast

The magnitude of backward masking is usually found to vary inversely with the amount of information about a target that is made available to the visual system. Contrary to these findings, we report a nonmonotonic relation between the magnitude of backward pattern masking and target duration. Specifically, masking decreased as target duration was increased to about 8 msec and, then, became more severe as target duration was further increased to a value of at least 40 msec. The occurrence of the nonmonotonic function depended on (a) the degree of definition of the target's edges, (b) the luminance levels within the target stimulus, and (c) the state of adaptation of the eye. It is hypothesized that the source of the nonmonotonic function was metacontrast interference that originated from within the target stimulus configuration. This hypothesis was supported by data that indicated that in the absence of any mask presentations, the apparent contrast between the target and its immediate background varied as a nonmonotonic function of target duration.     

Semantic processing without conscious identification: Evidence from event-related potentials.

Three event-related potential (ERP) experiments examined whether semantic content can be accessed from visually presented words that cannot be consciously identified. Category labels were shown to participants, followed by masked, briefly exposed words that were either exemplars of the category or not exemplars. The task was to verify the category, by guessing if necessary, and to identify the word, naming it if possible. Exposure durations were selected to allow identification in approximately half the trials. For identified words, there was a marked difference in the ERP response between in-category and out-of category words because of an N400 component. For unidentified words, there was a similar although smaller difference. Conscious identification was defined using a variety of approaches: verbal report, 6-alternative forced choice, and binary categorization (in the context of the regression method; A. G. Greenwald, M. R. Klinger, & E. S. Schuh, 1995). By any definition, ERPs for unidentified words showed evidence of semantic processing. In addition, there were differences in the neuronal populations recruited to process above-threshold versus below-threshold words, suggesting qualitative differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of displacement discrimination with and without perceived movement.

Investigated the similarity of reference effects for different delay conditions by testing the independence of reference and delay effects in 4 experiments, using 5 young adult observers. The critical independence property was whether the spatial variables (displacement separation from the visual reference) combined independently of the temporal variable (delay). This kind of independence did not hold for displacement discrimination at delays of 50 msec and 2,000 msec. When a test for the independence property was conducted at delays of 500 msec and 4,000 msec, observers reported no perceived movement. For these longer delays, the property was satisfied. These results are discussed using the general concept of a psychophysical mechanism. Such a mechanism combines the effects of several stimulus variables into a single mediating representation. By this analysis, at least 2 mechanisms must mediate the reference effect on displacement discrimination, one for delays of 200 msec and less and another for delays of 500 msec and more. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Backward masking.

In backward masking, perception of a test stimulus is suppressed by masking stimulation that is presented subsequently. Psychophysical studies of this phenomenon have utilized visual, auditory, and cutaneous stimuli. These masking studies are reviewed and their results discussed in terms of possible neural mediating mechanisms. (88 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intravenous cocaine induces platelet activation in the conscious dog

BACKGROUND: Cocaine consumption has been associated with thrombosis of coronary and peripheral arteries. Since cocaine has been found to induce platelet activation in vitro, we sought to establish whether cocaine induced platelet activation in vivo. METHODS AND RESULTS: Chronically instrumented, conscious dogs were infused with cocaine (1 mg/kg), norepinephrine (0.2 to 0.4 mg/kg), or saline intravenously over 1 minute. Activated canine platelets were identified in whole blood collected from an indwelling aortic catheter by flow cytometric detection of the binding of a monoclonal antibody directed against the activation-dependent antigen P-selectin. Infusion of cocaine resulted in an elevation of mean arterial pressure (91 +/- 3 to 128 +/- 7 mm Hg [P < .01]) and heart rate (87 +/- 9 to 125 +/- 11 beats per minute [P < .01]). A similar change (P = NS) in mean arterial pressure followed norepinephrine infusion (100 +/- 5 to 137 +/- 13 mm Hg [P < .04]), whereas saline infusion had no effect. Cocaine resulted in a substantial but delayed increase in platelet P-selectin expression (14 +/- 7% [P < .08], 31 +/- 12% [P < .04], and 55 +/- 22% [P < .04] at 17, 22, and 27 minutes after drug infusion, respectively). The magnitude of this increase was similar to that found in blood treated ex vivo with the agonists ADP or PAF (23 +/- 7% and 53 +/- 15%, respectively). No significant increase in P-selectin expression was detected in the blood of animals that received norepinephrine or saline. Serum cocaine concentrations were highest immediately after infusion (538 +/- 55 ng/mL at 2 minutes) but declined rapidly (185 +/- 22 and 110 +/- 25 ng/mL at 17 and 32 minutes after infusion); in contrast, the increase in benzoylecgonine concentrations was delayed (from < 25 ng/mL in all but one animal [34 ng/mL] at 2 minutes to 46 +/- 4 and 71 +/- 11 ng/mL at 17 and 32 minutes, respectively, after infusion). CONCLUSIONS: Intravenous cocaine induces activation of individual circulating platelets; this effect is not reproduced by infusion of norepinephrine at doses sufficient to exert similar hemodynamic effects. The delay in detection of activated platelets after treatment with cocaine may result from the adhesion and subsequent detachment of activated platelets; alternatively, cocaine metabolites, rather than the drug itself, may induce platelet activation.     

Metacontrast masking in amblyopia.

Measured the time course of visual signals arising from each eye of 4 strabismic and/or anisometropic amblyopes and 2 visually normal Ss using monoptic metacontrast masking. The amblyope Ss had 1 nonamblyopic eye, clear ocular media, and normal fundi. The method involved the brightness estimation of a high-contrast disk target whose visibility varied as a function of the stimulus onset asynchrony (SOA) of a subsequent annular mask. Results indicate that the SOA of optimal masking was delayed in the amblyopic eye compared to that of the fellow nonamblyopic eye or with normal eyes. The smaller the target, the greater was this SOA difference and the broader was the amblyopic U-shaped masking function. This finding is discussed in terms of the current model of metacontrast and represents the differential effect of the amblyopic process on human sustained and transient neurons. (French abstract) (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intelligence and information processing during an auditory discrimination task with backward masking: An event-related potential analysis.

The relation between mental ability and auditory discrimination ability was examined by recording event-related potentials from 60 women during an auditory oddball task with backward masking. Across conditions that varied in intensity and in the interval between the target and masking stimuli, the higher ability (HA) group exhibited greater response accuracy, shorter response times, larger P3 amplitude, and shorter P3 latency to target stimuli than the lower ability (LA) group. When instructed to ignore the stimuli, the HA group exhibited shorter mismatch negativity latency to deviant tones than the LA group. The greater speed and accuracy of auditory discrimination for the HA group, observed here with multiple measures, is not a consequence of response strategy, test-taking ability, or attention deployment. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Current concerns in visual masking.

Theories of emotion postulate that emotional input is processed independently from perceptual awareness. Although visual masking has a long tradition in studying whether emotional pictures are processed below a supposed threshold of perceptual awareness (subliminal perception), a consensus has yet to be reached. This article reviews current concerns in the use of visual masking. These include a reliable presentation method, the role of masking pictures, common definitions of awareness and their problems, current models of awareness, and neural mechanisms. A useful strategy may be the study of dose-response relationships between awareness and emotion processing that avoids a dichotomous view of awareness and allows conclusions about the relative independence of emotional processing from awareness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective forward masking.

Assessed the effects of masking on recall accuracy in 2 experiments with a total of 28 male undergraduates. When a patterned masking stimulus was presented immediately before a centrally-fixated, tachistoscopically-presented 7-letter row (forward masking), a selective effect on recall accuracy was found, as measured by a partial-report technique. There was greater masking of the end letters than of the center letters in the displays. When the masking stimulus was presented immediately after the presentation of a letter row (backward masking), the results confirmed previous findings of greater masking of the center letters than the end letters. These different selective effects of forward and backward masking are consistent with the assumption that the processing of multiletter displays begins at the ends of the letter rows. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Practice effects in backward masking.

In two experiments we demonstrate that much larger practice effects occur in a backward masking paradigm where patterned masks are used than in similar visual processing paradigms, such as lateral masking and whole report. In additional experiments we examine four possible explanations for the large practice effects: increased familiarity with the paradigm in general, learning about the targets, learning about the masks, and enhanced sensory processing. Because of failure to observe similar practice effects in related paradigms not involving backward masking and because of the sustained nature of the improvement, we reject the first explanation as a source of practice effect. Experiment 3 allowed us to reject target learning as a source of improvement as well; target sets were switched at the end of training, but no decrement in performance was observed. In Experiment 4, mask sets were switched at the end of training, revealing a significant decrement in performance. Learning about the specific masks, then, does contribute to the observed improvement. However, it is responsible for only about one third of the overall improvement in performance. The final experiment provides evidence that the residual improvement is due to enhanced sensory processing. In that experiment, training on backward masking led to a lowered threshold in a two-flash paradigm but not to a significant change in whole-report performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monitoring, activation, and disinhibition: Effects of white noise masking on spoken thought.

2experiments with 20 male and 20 female adults each and 2 replications tested the hypothesis that preventing a person from hearing himself as he speaks results in disinhibition of communication thought. White noise masking (WNM) was used to prevent S from hearing himself as he spoke. TAT stories and Holtzman Inkblot Test (HIT) responses were the main dependent variables. Under WNM, TAT stories showed more impulse-dominated themes and fewer defensively modulated stories than under normal conditions (N). The effect was exaggerated when WNM followed N. Female Ss produced more color responses on HIT under WNM than under N, an effect that was augmented when WNM followed N. Under WNM, physical properties of voices changed lawfully: pitch and intensity rose and phonation time increased, but the increase was greater for spontaneous speech than for read speech. WNM resulted in a disinhibition of drive-related fantasies that had already been primed. Interfering with the monitoring of one's vocal activity by itself does not necessarily result in impairment of thought organization or of reality attunement. The results have bearing upon a theory of monitoring, activation of impulse-relevant content, and disinhibition of spoken language. (28 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conceptual masking in brief visual displays.

Examined a paradigm used to study conceptual masking. This paradigm uses a variant of the partial report procedure, wherein a display of characters is preceded or followed by a probe character and Ss must report whether the probe was in the display or not. Ss were 7 undergraduates. Results show that neither specific orienting effects of the probe nor eye movements to the probe character could explain the pattern of data found in earlier studies (V. Di Lollo and M. Moscovitch; see record 1984-14011-001). Data are discussed in the context of P. Dixon's (see record 1986-21077-001) model of performance within this paradigm. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)