A behavioral study of temporal processing and visual persistence in young and aged rats.

Young rats were presented with light flash prepulses varying in duration from 1 to 128 msec, with light offset or light onset fixed at 70 msec prior to an acoustic startle stimulus (Experiment 1A), and, with single or paired 1-msec flashes, the 2nd (or only) flash given 100 to 500 msec before the startle, and 1 msec to 400 msec interflash intervals (Experiment 1B). Older rats (10 and 20 mo old) received the same single and double flashes but with the maximum interflash interval extended to 1,500 msec (Experiment 2). Reflex inhibition increased with increased duration from 1 to 8 msec and decreased as light onset progressively exceeded 100 msec. Inhibition for both single and double flashes also declined for onset lead times beyond 100 msec, then increased for a double flash once the interflash interval exceeded 100 msec in young and middle-aged rats and 1,500 msec in the oldest rats. Peak inhibition was much reduced in the oldest rats at short lead times but was greater than that of younger rats at long lead times. These data suggest that aged rats process visual stimuli more slowly than younger rats and show poorer temporal acuity coupled with greater visual persistence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of temporal integration on the shape of visual backward masking functions.

Many studies of cognition and perception use a visual mask to explore the dynamics of information processing of a target. Especially important in these applications is the time between the target and mask stimuli. A plot of some measure of target visibility against stimulus onset asynchrony is called a masking function, which can sometimes be monotonic increasing but other times is U-shaped. Theories of backward masking have long hypothesized that temporal integration of the target and mask influences properties of masking but have not connected the influence of integration with the shape of the masking function. With two experiments that vary the spatial properties of the target and mask, the authors provide evidence that temporal integration of the stimuli plays a critical role in determining the shape of the masking function. The resulting data both challenge current theories of backward masking and indicate what changes to the theories are needed to account for the new data. The authors further discuss the implication of the findings for uses of backward masking to explore other aspects of cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional capture by abrupt onsets: New perceptual objects or visual masking?

The authors have shown that an object appearing abruptly in a previously blank location is efficiently detected in visual search when it is embedded in an array of objects without abrupt onset (termed no-onset stimuli). In these experiments, no-onset stimuli appeared well before the onset stimulus but were camouflaged by additional line segments rendering the stimuli unidentifiable. B. S. Gibson (see record 1997-06229-001) claims that the availability of the no-onset stimuli was delayed relative to that of the abrupt onset stimulus because of forward masking. The authors show that forward masking is unlikely to be a significant factor in their experiments, and 3 new experiments are reported that undermine Gibson's masking account. Observed differences in the efficiency with which onset and no-onset stimuli are processed in visual search are due to attentional capture by new perceptual objects and to a relatively sluggish process of updating existing object representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual Grouping by Motion Precedes the Relative Localization Between Moving and Flashed Stimuli.

A flashed stimulus is perceived as spatially lagging behind a moving stimulus when they are spatially aligned. When several elements are perceptually grouped into a unitary moving object, a flash presented at the leading edge of the moving stimulus suffers a larger spatial lag than a flash presented at the trailing edge (K. Watanabe. R. Nijhawan. B. Khurana, & S. Shimojo. 2001). By manipulation of the flash onset relative to the motion onset, the present study investigated the order of perceptual operations of visual motion grouping and relative visual localization. It was found that the asymmetric mislocalization was observed irrespective of physical and/or perceptual temporal order between the motion and flash onsets. Thus, grouping by motion must be completed to define the leading-trailing relation in a moving object before the visual system explicitly represents the relative positions of moving and flashed stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Linearity and normalization in simple cells of the macaque primary visual cortex

Simple cells in the primary visual cortex often appear to compute a weighted sum of the light intensity distribution of the visual stimuli that fall on their receptive fields. A linear model of these cells has the advantage of simplicity and captures a number of basic aspects of cell function. It, however, fails to account for important response nonlinearities, such as the decrease in response gain and latency observed at high contrasts and the effects of masking by stimuli that fail to elicit responses when presented alone. To account for these nonlinearities we have proposed a normalization model, which extends the linear model to include mutual shunting inhibition among a large number of cortical cells. Shunting inhibition is divisive, and its effect in the model is to normalize the linear responses by a measure of stimulus energy. To test this model we performed extracellular recordings of simple cells in the primary visual cortex of anesthetized macaques. We presented large stimulus sets consisting of (1) drifting gratings of various orientations and spatiotemporal frequencies; (2) plaids composed of two drifting gratings; and (3) gratings masked by full-screen spatiotemporal white noise. We derived expressions for the model predictions and fitted them to the physiological data. Our results support the normalization model, which accounts for both the linear and the nonlinear properties of the cells. An alternative model, in which the linear responses are subject to a compressive nonlinearity, did not perform nearly as well.     

Electrophysiological evidence for the "missing link" in crossmodal attention.

Notes that orienting attention involuntarily to the location of a sensory event influences responses to subsequent stimuli that appear in different modalities with one possible exception; orienting attention involuntarily to a sudden light sometimes fails to affect responses to subsequent sounds (e.g., C. Spence and J. Driver, 1997). Here the authors investigated the effects of involuntary attention to a brief flash on the processing of subsequent sounds in a design that eliminates stimulus–response compatibility effects and criterion shifts as confounding factors. 13 18–31 yr olds participated in the study. In addition, the neural processes mediating crossmodal attention were studied by recording event-related brain potentials. The data show that orienting attention to the location of a spatially nonpredictive visual cue modulates behavioral and neural responses to subsequent auditory targets when the stimulus onset asynchrony is short (between 100 and 300 ms). These findings are consistent with the hypothesis that involuntary shifts of attention are controlled by supramodal brain mechanisms rather than by modality-specific ones. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Direct estimates of the apparent duration of a flash.

Substantial evidence now shows that visual persistence can extend the apparent duration of a brief stimulus flash by several hundred msec. A technique of G. Sperling's was applied in which S adjusts a click to coincide, 1st with the apparent onset of a flash, and then with its apparent offset. The interclick interval thus determined is used as a measure of the apparent duration of the flash. Visual persistence is shown when the interclick interval exceeds the actual stimulus duration. When the flash and adapting field luminances were the same, persistence reached 175 msec. for brief flashes (10 msec.), decreased to 60 for longer ones (200 msec.), and was negligible for flashes exceeding 500 msec. When a visual noise field followed the postadaptation field, persistence was determined entirely by the time from the flash offset to noise onset, up to about 200 msec. Beyond that, the noise onset had no effect, presumably because the persistence had already ceased before the noise arrived. Conditions without visual noise, but with different combinations of pre- or postadaptation field, also produced substantial changes in visual persistence. Results show that (a) visual persistence can be estimated rather directly by this technique; (b) persistence is sensitive to adaptation conditions; and (c) visual noise will terminate persistence. Results support a process-stopping interpretation of information processing by visualoise, as distinct from a sensory integration view. (French summary) (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Continuous measurement of visible persistence.

In the synchrony judgment paradigm, Ss judge whether a click precedes or follows the onset of a light flash and, on other trials, whether or not a click precedes light termination. The interclick interval defines the duration of visible persistence. An elaboration of this method was developed that consisted of 2 phases: In Phase 1, the luminance of a reference stimulus was psychophysically matched to the peak brightness of the test flash. Five luminance values between .1 and 1.0 of the reference stimulus were used subsequently. In Phase 2, a random 1 of the 5 reference stimuli, a test flash, and a click were presented; the Ss judged whether the click occurred before or after the brightness of test flash reached the reference value (on onset trials) or decayed below it (on termination trials). This method was validated on 3 male graduate students with test stimuli whose luminance rose and decayed slowly in time, and then was used to trace out the precise subjective rise and decay (temporal brightness response function) of brief flashes. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The backward masking red light effect in schizophrenia: Relationship to clinical features and neurocognitive performance.

The “backward masking red light effect” involves a change in visual backward masking performance with a red (compared with a green or gray) background that is in the opposite direction relative to nonpsychiatric controls. This effect has been previously reported in individuals with schizophrenia, their first-degree relatives, and a schizotypy sample. The current study provides the first examination of the relationship of this effect with clinical and neurocognitive measures in a new sample of higher functioning patients with schizophrenia. A location backward masking by pattern task was administered to 16 outpatients with schizophrenia and 21 nonpsychiatric controls. The task was presented on red, green, and gray backgrounds. There was a significant group by color interaction at the 60-ms stimulus onset asynchrony: Participants with schizophrenia tended to decrease accuracy with a red (compared with a gray) background, whereas controls tended to increase accuracy. This interaction remained significant after covarying for baseline (gray) backward masking accuracy. In the schizophrenia patients, a decrease in backward masking accuracy to the red background was correlated with more negative symptoms, lower estimated premorbid IQ, and greater color–word Stroop interference but was not related to positive or disorganized symptoms, age of onset, duration of illness, digit symbol coding performance, or baseline (gray) backward masking accuracy. In contrast, there was no relationship between the red light change score and any of the neurocognitive variables in the control group. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Reduction of all-trans-retinal limits regeneration of visual pigment in mice

Absorption of photons by pigments in photoreceptor cells results in photoisomerization of the chromophore, 11-cis-retinal, to all-trans-retinal and activation of opsin. Photolysed chromophore is converted back to the 11-cis-configuration via several enzymatic steps in photoreceptor and retinal pigment epithelial cells. We investigated the levels of retinoids in mouse retina during constant illumination and regeneration in the dark as a means of obtaining more information about the rate-limiting step of the visual cycle and about cycle intermediates that could be responsible for desensitization of the visual system. All-trans-retinal accumulated in the retinas during constant illumination and following flash illumination. Decay of all-trans-retinal in the dark following constant illumination occurred without substantial accumulation of all-trans-retinal, generated by constant approximately equal to visual pigment regeneration (t1/2 approximately 5 and t1/2 approximately 7 min, respectively). All-trans-retinal, generated by constant illumination, decayed approximately 3 times more rapidly than that generated by a flash and, as shown previously, the rate of rhodopsin regeneration following a flash was approximately 4 times slower than after constant illumination. The retinyl ester pool (> 95% all-trans-retinyl ester) did not show a statistically significant change in size or composition during illumination. In addition, constant illumination increased the amount of photoreceptor membrane-associated arrestin. The results suggest that the rate-limiting step of the visual cycle is the reduction of all-trans-retinal to all-trans-retinol by all-trans-retinol dehydrogenase. The accumulation of all-trans-retinal during illumination may be responsible, in part, for the reduction in sensitivity of the visual system that accompanies photobleaching and may contribute to the development of retinal pathology associated with light damage and aging.     

Functional Rescue of photoreceptors from the damaging effects of constant light by survival-promoting factors in the rat

PURPOSE: To investigate whether and how survival-promoting agents rescue photoreceptor cell function and morphology from constant light damage, the authors recorded electroretinographic (ERG) responses and examined light micrographs of retinas in those rats given intravitreal injection of midkine (MK) and basic fibroblast growth factor (bFGF) before constant exposure. METHODS: Albino Sprague-Dawley rats were injected with MK, bFGF, or phosphate-buffered saline (PBS) 2 days before the onset of 1 week of constant light. ERG responses were recorded using white flash stimuli with the intensity range of 4 log units, followed by histologic examinations of retinas, including quantitative assessment of the outer nuclear layer thickness as an index of photoreceptor cell loss. RESULTS: ERG responses were barely detectable in uninjected eyes after 1 week of constant light. On the other hand, distinct responses were recordable in eyes injected intravitreally with MK and bFGF, and the degree of ERG rescue in terms of the amplitude of b-wave was approximately 40% to 60% compared with normal eyes. Intravitreally injected PBS showed slight, but noticeable, preservation of ERG responses as well. Histologic examination revealed that MK and bFGF protected photoreceptors from light damage. A good correlation was found between anatomic rescue of photoreceptors as assessed by outer nuclear layer thickness and the functional rescue as defined by the magnitude of ERG responses. CONCLUSIONS: Functional and anatomic rescue of photoreceptors in albino rats from constant light damage is achieved by prior intravitreal injection of MK and bFGF.     

Size Estimation in Schizophrenics as a Function of Stimulus-Presentation Time.

15 good premorbid paranoid acute schizophrenics, 15 poor premorbid nonparanoid acute schizophrenics, and 15 attendants, all males, estimated stimulus paranoid size after receiving (a) 10-sec. and (b) 100-msec. presentations of the standard, also (c) 10-msec. blank flashes instead of the standard. Choices were then made from a group of variable-sized stimuli. As expected, good paranoids, normals, and poor nonparanoids tended to low, intermediate, and high estimation levels, respectively. Contrary to eye-movement interpretation, patient groups differed under the 100-msec. presentation. Lowered estimation level with this presentation suggested stimulus redundancy interpretations. No differences with the blank flash ruled out a simple size-preference response bias. Equal proportions of "hits" among groups indicated that error distributions rather than error frequencies accounted for the results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral and computational models of spatial attention.

Pigeons pecked for food in a spatially cued choice reaction time (RT) task. A brief (50-msec) white light appeared on a left or right key and probabilistically predicted the location (on either the left or right key) of a subsequent target stimulus. The time between cue and target onset (stimulus onset asynchrony), the base rate of left cues, and the probability that the cue correctly predicted the target (cue validity) were experimentally varied. The mean RT to respond to the target key was faster on correctly cued trials (defining a validity effect), decreased for both valid and invalid trials as stimulus onset asynchrony increased (defining an alerting effect), showed a variety of base-rate effects, and did not depend on cue validity. It is shown with a computational-processing model that dynamic interactions of short-term and associative memory processes are sufficient to produce these attention-like empirical phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Judgments of synchrony between auditory and moving or still visual stimuli.

The flash-lag effect is a visual illusion wherein intermittently flashed, stationary stimuli seem to trail after a moving visual stimulus despite being flashed synchronously. We tested hypotheses that the flash-lag effect is due to spatial extrapolation, shortened perceptual lags, or accelerated acquisition of moving stimuli, all of which call for an earlier awareness of moving visual stimuli over stationary ones. Participants judged synchrony of a click either to a stationary flash of light or to a series of adjacent flashes that seemingly bounced off or bumped into the edge of the visual display. To be judged synchronous with a stationary flash, audio clicks had to be presented earlier--not later--than clicks that went with events, like a simulated bounce (Experiment 1) or crash (Experiments 2-4), of a moving visual target. Click synchrony to the initial appearance of a moving stimulus was no different than to a flash, but clicks had to be delayed by 30-40 ms to seem synchronous with the final (crash) positions (Experiment 2). The temporal difference was constant over a wide range of motion velocity (Experiment 3). Interrupting the apparent motion by omitting two illumination positions before the last one did not alter subjective synchrony, nor did their occlusion, so the shift in subjective synchrony seems not to be due to brightness contrast (Experiment 4). Click synchrony to the offset of a long duration stationary illumination was also delayed relative to its onset (Experiment 5). Visual stimuli in motion enter awareness no sooner than do stationary flashes, so motion extrapolation, latency difference, and motion acceleration cannot explain the flash-lag effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cortical dynamics of lateral inhibition: Metacontrast masking.

The dynamic properties of a neural network model of visual perception, called the boundary contour system, explain characteristics of metacontrast visual masking. Computer simulations of the model, with a single set of parameters, demonstrate that it accounts for 9 key properties of metacontrast masking: Metacontrast masking is strongest at positive stimulus onset asynchronies (SOAs); decreasing target luminance changes the shape of the masking curve; increasing target duration weakens masking; masking effects weaken with spatial separation; increasing mask duration leads to stronger masking at shorter SOAs; masking strength depends on the amount and distribution of contour in the mask; a second mask can disinhibit the masking of the target; such disinhibition depends on the SOA of the 2 masks; and such disinhibition depends on the spatial separation of the 2 masks. No other theory provides a unified explanation of these data sets. Additionally, the model suggests a new analysis of data related to the SOA law and makes several testable predictions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamic contrast perception assessed by pattern masking

The perceived contrast of a pulsed grating varies markedly with the exposure duration and spatial frequency of the grating. We studied dynamic changes in perceived grating contrast with a pattern-masking paradigm. We measured masking of a brief, localized test pattern (a D6 stimulus, 30 ms in duration) by fixed-contrast cosine grating patterns of varying duration (50-500 ms). The cosine mask pattern had spatial frequency of either 1 or 6 cycles per degree (cpd) at a contrast of 0.3. The D6 test pattern was centered on a light bar of the mask and was either positive peak contrast (same-polarity test and mask) or negative peak contrast (opposite-polarity test and mask). In Experiment 1, the test and mask had simultaneous onset. With a 6-cpd mask, the same-polarity test-threshold elevation versus mask-duration function increases monotonically. For a 1-cpd mask, the same-polarity threshold-mask-duration function is nonmonotonic, with peak masking effect produced by a grating pulse of 80-100 ms. These masking effects are closely congruent with known dynamic contrast effects. With negative tests, masking-duration functions are elevated from same-polarity functions and are essentially similar in shape for 1- and 6-cpd masks. The elevated thresholds suggest inhibitory interaction between ON and OFF pathways, with a similar time course across spatial frequency. In Experiment 2, the D6 test was delayed from mask onset by 33 ms. Positive contrasts only were employed. For 1-cpd stimuli, the delay of test greatly reduced masking at all mask durations and eliminated the nonmonotonic function. This suggests that for low-spatial-frequency patterns, perceived contrast is determined by an early peak component of the neural response. But for 6-cpd stimuli, masking of the delayed test was somewhat greater at all mask durations, consistent with a gradually increasing underlying neural response to the grating. Finally, in Experiment 3, same-polarity masking effects at both spatial frequencies were replicated with negative-contrast test and mask (OFF pathway mediation). This indicates that the ON and OFF pathways have similar response dynamics.     

A theory of visual information acquisition and visual memory with special application to intensity-duration trade-offs.

Describes a theory of memory for visual material in which the visual system acts as a linear filter operating on a stimulus to produce a function, a(t), relating some sensory response to t (the time since stimulus onset). Stimulus information is acquired at a rate proportional to the product of the magnitude by which a(t) exceeds some threshold, and the amount of as-yet-unacquired information. Recall performance is assumed to equal the proportion of acquired information. The theory accounts for data from 2 digit-recall experiments in which stimulus temporal waveform was manipulated. The authors comment on the theory's account of the relation between 2 perceptual events: the phenomenological experience of the stimulus, and the memory representation that accrues from stimulus presentation. It is asserted that these 2 events, although influenced by different variables, can be viewed as resulting from 2 characteristics of the same sensory-response function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prognostic relevance of urokinase plasminogen activator detection in micrometastatic cells in the bone marrow of patients with primary breast cancer

The "attentional model" of time estimation assumes that temporal judgments depend on the amount of attention allocated to the temporal processor (the timer). One of the main predictions of this model is that an interval will be judged shorter when attention is not allocated to the temporal parameters of the task. Previous studies combining temporal and nontemporal tasks (dual-task method) have suggested that the time spent processing the target duration might be a key factor. The less time devoted by the subject to the temporal task, the shorter the judged duration. In the two experiments presented here, subjects were asked to judge both the duration of a visual stimulus and an increment in intensity occurring at any time during this stimulus. In the second experiment, trials without intensity increments were added. The main result is that the judged duration was shorter when the increment occurred later in the stimulus or did not occur. In those cases, subjects had been expecting increment occurrence during most part of the stimulus and thus had focused for a shorter time on stimulus duration. We propose that attention shifts related to expectancy and to detection of the increment reduce subjective duration.     

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)