U-shaped masking functions in visual backward masking: Effects of target configuration and retinal position

Printed letters were found to become increasingly susceptible to visual backward masking when presented to one side of the point of fixation: All masking was found to be a u-shaped function of the time interval separating the offset of the target from the onset of the masking figure. The interval at which maximum masking was observed, as well as the amount of masking observed, varied with the target-mask configuration studied. More masking was found when the ISI field was lighted than when it was not.     

Metacontrast and brightness discrimination

An attempt was made to obtain U-shaped masking functions in two metacontrast experiments. Trained Ss judged whether a square test stimulus (TS) was bright or dim. The TS was presented alone or in conjunction with an adjacent pair of square masking stimuli (MS) whose energy equaled the bright TS. The stimulus onset asynchronies (SOA) rangedfrom 0 to 125 msec. The task minimized the role of apparent movement cues as a reliable basis for judgrnent. Similar studies have employed TS plus MS vs MS alone as the alternatives, allowing apparent movement to be a cue. Brightness accuracy was a U-shaped function of SOA. This finding is consistent with neural-net models (Weisstein, 1968). However, analysis of Ss’ response bias suggested an alternative explanation involving the MS as a comparison stimulus at short SOA. It was concluded that U-shaped masking functions are also consistent with theories based upon independent component processes, e.g., Schurman and Eriksen (1970) and Uttal (1970).     

Laterality differences and practice effects under central backward masking conditions

Two experiments were conducted to examine laterality differences and practice effects under various central backward masking conditions. Critical stimulus onset asynchrony (SOA) was determined for subjects on 3 consecutive days using single letters as target stimuli (TS) and a pattern masking stimulus (MS). There was a right visual field (RVF) advantage on Day 1 but no difference between the visual fields on following days. The decline in the RVF advantage appeared to be dependent upon prior experience with laterally located letters, to be independent of initial experience with a particular set of letters, and to be more pronounced for females than for males. In addition, large improvements in performance were found, particularly between the first and second testing sessions. These practice effects were discussed in terms of the possible development of strategies for enhancing TS features or attenuating MS features.     

An analysis of U-shaped metacontrast

Using a brightness-discrimination task similar to that employed by Bernstein, Proctor, Proctor, and Schurman (1973), masking functions were obtained in two experiments. In Experiment I, test stimulus (TS) and mask stimulus (MS) energies were held constant but luminance and duration were varied reciprocally. The obtained masking functions, plotted as a function of stimulus onset asynchrony (SOA), were of an essentially identical U shape. This suggests that (a) SOA is a more suitable measure of delay than interstimulus interval, and (b) Bloch’s law holds for the requisite discrimination. In Experiment II, TS luminance and MS luminance were varied independently. This was to see whether the MS served as a frame of reference at short SOA, as suggested previously (Bernstein et al, 1973). The results were that this was, in fact, the case and that the transition from comparative to absolute judgment strategies as SOA increases is a major contributor to U-shaped masking functions.     

The recovery of a visually masked target

Ss were briefly shown pairs of letters under backward masking and disinhibitive backward masking conditions. For the backward masking condition, a single homogeneous flash of light (M1), varying in duration, followed the presentation of letters after a varying delay (IS11), and recognition of the target letters (TS) was found to be a function of M1 duration and ISI1. For the disinhibition condition, a variable second mask (M2) followed M1 after a variable delay (ISI2) and disinhibition of M1’s effect on TS recognition occurred. Provided the ISIs were adequate, a relatively powerful M2 wass found to disinhibit a moderate Ml’s effect on the TS. Current theories of visual masking were examined in the light of these findings.     

Anatomy of a flash. 1. Two-peak masking and a temporal filling-in

A modified paradigm of Crawford masking was used to link masking to brightness fluctuation, as distinct from flash brightness. Thresholds were measured for a 10 ms incremental pulse (the 'probe') presented before, during, or after a 500 ms pulse (the 'flash'). Both pulses were spatially coextensive with the background field, thus the criterion for probe detection was purely temporal. The flash occurred either in the tested eye, the opposite eye, or in both eyes. In all conditions, masking was strongly bimodal: thresholds peaked near flash onset and flash offset. The flash was perceived as a unitary event. Bimodal masking is attributed to cortical on-and off-effects, as (i) dichoptic masking was strong and (ii) the same incremental probe was masked by either incremental or decremental flashes. Strikingly, monocular probe thresholds were about equally elevated by binocular as by monocular flashes, although the binocular flashes were brighter. Therefore, some monocular features can be preserved in the larger net binocular response. A general conclusion is that masking depends on the same transient neural responses that bring about a brightness fluctuation, whereas the appearance of the flash as a single event, a unitary change of brightness, depends on a different mechanism, perhaps a sustained response that performs a temporal filling-in.     

Visual storage or visual masking? an analysis of the “retroactive contour enhancement” effect

Standing and Dodwell (1972) reported that a contoured target stimulus which is only poorly identified when exposed briefly against a steady background field can be identified accurately if the field is terminated shortly after target offset. This observation was confirmed and, in addition, it was shown that target identification is enhanced when the field is initiated shortly before target onset. Furthermore, it was demonstrated that a continuous background field is not essential for either effect. It was argued that these “retroactive” and “proactive” enhancements of target identification were due to a complex interaction among forward, backward, and simultaneous masking.     

The effect of a red background on location backward masking by structure

It has been established that diffuse red light partially suppresses the magnocellular (M) visual pathway. Previous research reported that metacontrast masking is reduced (improved accuracy) with a red background, consistent with a reduction in M pathway response from the mask. In contrast, a recent study used location backward masking by noise and found that accuracy decreased with a red background--theoretically due to suppression of the M pathway's initial localization of the target. The present study provides the first report examining the effect of red light on performance in a location backward masking by structure task. Results revealed a main effect of a red (as opposed to a green) background on reducing masking (improved accuracy) with a medium effect size (eta2 = .23). This effect was strongest at the 47- and 60-msec stimulus onset asynchronies. Results suggest that red light primarily decreases interference from the mask in location backward masking by structure.     

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.     

Spatial disinhibition of orientation analyzers

Following the successive presentation of two masking gratings (M1 and M2), subjects were required to detect the presence or absence of a single vertical line (TS). When the orientations of the two masks were optimal, M1 was able to reduce the masking effect of M2 on the TS. For a vertical TS, disinhibition was maximal when the orientations of M1 and M2 were similar and was minimal when the orientational difference was greater than 15 deg. It is suggested that the spatial selectivity of the disinhibition function reflects the activity of neurons tuned to orientation, and that the disinhibition masking paradigm may be a useful psychophysical technique to measure tuning functions of other feature detectors.     

An illusion of reversed direction in hyperopes

If a subject who is sufficiently farsighted removes his corrective, positive, lenses and looks with one eye from a distance of one or a few meters, at a small lighted area such as the (continuously "on") indicator light of an electric toothbrush, razor, or smoke detector, and if a small object such as a pin is then moved slowly from above to below the subject's eyes (in a plane close to the eye), the subject will perceive the object moving normally from above to below until it encroaches on his view of the lighted area. The object will then be seen to encroach first on the bottom of the lighted area, and as the object continues to move down it will be seen to be moving up across the lighted area, exiting the lighted area at the top. Similarly, an object moved in front of the eye from the subject's left to his right will be seen by the subject to traverse the lighted area in the reverse direction, right to left, even though the subject moves the object himself. Also, while the object is in front of the lighted area, it is perceived as an upside down silhouette having surprisingly clear and sharp edges, and it appears to be located on the lighted area rather than close to the eye where it really is.     

Binaural interaction in backward masking

The binaural auditory system exhibits certain advantages over the monaural system when detecting a tonal signal in a background of masking noise. These advantages have been described in detail and are referred to as masking-level differences, or MLDs. It has been demonstrated, for example, that performance in detecting a tonal signal that has been reversed in phase at one ear relative to the other ear is about 15–17 dB better than detection of the same signal in-phase at the two ears when masked by moderately intense masking noise that is in-phase at the two ears. The explanations for this phenomenon fall into two general categories, and both types of explanations are based upon the interaction of the tonal signal and masker when they are added together. In the present paper, data are presented which indicate that an MLD of at least 4–5 dB can be obtained in a binaural masking experiment in which the offset of the tonal signal precedes the onset of the noise masker.     

Anatomy of a flash. 2. The 'width' of a temporal edge.

In a previous study it has been found by using the Crawford masking paradigm with spatially coextensive stimuli that the end points of even a weak flash have a strong masking effect on the probe pulse, but no threshold elevation was observed when the probe was 100 ms or longer from flash onset and offset. The relationship between the strength of a temporal edge (eg the amplitude of a sudden increase in field luminance) and the duration of masking has not been systematically investigated. In the present experiments the duration of masking produced by a step of luminance as a function of step size was measured. With steps whose amplitude was between ten and five hundred times detection threshold, the duration of masking was about constant, ie 70 and 50 ms for on-responses and off-responses, respectively. This refractory period defined the 'width' of a temporal edge. Unless two suprathreshold unidirectional luminance changes are separated by an interval exceeding the width of a temporal edge, they are perceived as a single change in brightness. A linear systems analysis led to predictions for ramp stimuli that were confirmed by experiment.     

Neonatal tactile stimulation enhances spatial working memory, prefrontal long-term potentiation, and D1 receptor activation in adult rats

Environmental stimuli during neonatal periods play an important role in the development of cognitive function. In this study, we examined the long-term effects of neonatal tactile stimulation (TS) on spatial working memory (SWM) and related mechanisms. We also investigated whether TS-induced effects could be counteracted by repeated short periods of maternal separation (MS). Wistar rat pups submitted to TS were handled and marked transiently per day during postnatal days 2–9 or 10–17. TS/MS pups were stimulated in the same way as TS pups and then individually separated from their mother for 1 h/day. Their nontactile stimulated (NTS) siblings served as controls. In adulthood, TS and TS/MS rats showed better performance in two versions of the delayed alternation task and superior in vivo long-term potentiation of the hippocampo–prefrontal cortical pathway when compared with controls. Furthermore, there were more doses of A77636 (a selective dopamine D1 agonist) to significantly improve SWM performance in TS and TS/MS rats than in NTS rats, suggesting that activation of prefrontal D1 receptors in TS and TS/MS rats is more optimal for SWM function than in NTS rats. MS did not counteract TS-induced effects because no significant difference was found between TS/MS and TS animals. These data indicate that in early life, external tactile stimulation leads to long-term facilitative effects in SWM-related neural function.     

Finding lung nodules with and without comparative visual scanning

The effect of a pretarget (TS1) masked by a noise mask (MS) upon the recognition of a posttarget (TS2) was examined in a TS1-MS-TS2 paradigm. The results clearly showed that the presentation of TS1 masked completely by MS reduced the recognition of a subsequent TS2 to a much greater extent if TS2 was the same as TS1 than when it was not. The results suggest that a TS1 that is perceptually masked by an MS nevertheless continues to have an effect within the visual system. A possible explanation of this reductive effect is described briefly.     

Spatial selection in peripheral letter recognition: in search of boundary conditions

Recognition performance for a peripherally presented target letter embedded in a letter string is worse than for targets presented in isolation. This lateral masking effect is commonly attributed to impairments when identifying flanked letters. The hypothesis that also failures during spatial selection of the target underlie lateral masking effects was examined by varying the brightness of the flankers (Experiment 1), by cueing the target position at various times before, during, or after presentation of the string (Experiment 2) and by avoiding the abrupt on- and offset of the flankers (Experiments 3 and 4). Whereas the flankers' brightness had no effect on and cueing only slightly reduced the lateral masking effects, it was substantially reduced by avoiding the abrupt on- and offset of the flankers. The results show that spatial selection is impaired in peripheral vision, and that this is one important factor underlying lateral masking effects.     

Effect of “backward” masker fringe on the detectability of pulsed diotic and dichotic tonal signals

The effects of backward masker “fringe” on performance in homophasic and antiphasic masking conditions were investigated. The results of the study indicate that (1) the presence of a backward masker fringe has only a small effect on performance in homophasic masking conditions; (2) under antiphasic masking conditions, the presence of a backward masker fringe improves performance; (3) similar to the results of studies investigating the effects of forward masker fringe, the magnitude of the improvement in performance increases as the duration of the fringe increases; and (4) the magnitude of the improvement caused by the presence of backward masker fringe is considerably smaller than the magnitude of the improvement caused by the forward masker fringe. It appears, then, that the presence of backward masker fringe may provide a baseline or reference phase similar to that which the forward fringe is presumed to provide. The presence of this reference phase after the offset of the signal apparently makes the phase shift associated with the signal-plus-noise waveform more discernible, thus leading to higher detectability. However, for reasons not yet clear, the presence of a baseline or reference phase after the offset of the signal (backward fringe conditions) does not make the signal-plus-noise phase shift as discernible as do either the presence of that same reference phase before the onset of the signal (forward fringe condition) or the presence of that same reference phase both before signal onset and after signal offset (continuous masker condition).     

When the target becomes the mask: using apparent motion to isolate the object-level component of object substitution masking

J. T. Enns and V. Di Lollo (1997) discovered a new form of visual masking that they labeled object substitution masking (OSM). OSM occurs when 4 dots, presented around a target, trail in the display after target offset. The present study showed that the physical presence of the masking dots after target offset is not necessary for OSM. Instead, the continued presence of a changing high-level representation associated with the target suffices to yield OSM. Apparent motion was used to define such representation. In these experiments, the initial display offset and was followed by a 2nd display where masks appeared at new locations. Only when the spatiotemporal properties of the stimuli on the 2nd display supported the perception of the target moving and turning into the mask was OSM observed.     

INDUCED AVOIDANCE BEHAVIOUR IN THE PROTOZOA TETRAHYMENA

B ergstrom , S. R. Induced avoidance behaviour in the Protozoa Tetrahymena. Scand.J. Psychol ., 1968, 9, 215–219.—A sample of Tetrahymena, exposed to a series of light and electric shocks paired, was placed in a partially lighted glass chamber. During the first three minutes the number of animals in the lighted parts of the chamber decreased, and an essentially smaller proportion of the sample was then found in the light, in comparison with control samples, which had received either shocks or light or neither of the two stimuli.     

Selective masking and processing strategy

A patterned masking stimulus was presented immediately following a 100-ms exposure of a centrally-fixated, eight-letter row. The bar-marker probe, indicating which letter to report, appeared either at onset (simultaneous cue), or at offset (delayed cue) of a letter row. A selective-masking effect--greater masking at the centre positions than at the ends of a row--was obtained with the delayed cue. With the simultaneous cue, all positions were masked and there was no selective-masking effect. These results indicate that the effects of a patterned masking stimulus are dependent upon the processing strategy, and they support previous interpretations of selective masking which state that it is produced by an ends-first processing strategy.