Visual masking and the recovery phenomenon

Two experiments were carried out to investigate visual masking and target recovery. In the first experiment it was found that with superimposed disks of various sizes masking increases with increasing target-mask similarity and contour proximity. The results of the second study show that the extent of masking produced by a disk, which is slightly larger than the target, is drastically reduced when the mask in turn is followed by a ring, the inner contour of which is contiguous with the contour of the mask. This “facilitation effect” decreases as the interval between the mask and the third stimulus is increased. Target recovery in this situation appears to be brought about as a result of the reduction or elimination of the contour of the mask, which, as the first study has shown, is critical in bringing about the masking effect. The results are discussed in terms of some of the known physiological properties of the visual system.     

Visual aftereffects for walking actions reveal underlying neural mechanisms for action recognition

The results of this study illustrate a new high-level visual aftereffect: Observing actors walking forward, without horizontal translation, makes subsequent actors appear to walk backward, and the opposite effect is obtained after observing backward walking. We used this aftereffect, which cannot be explained by simple low-level adaptation to motion direction, to investigate the properties of neural mechanisms underlying recognition of walking actions. Our results suggest that the perception of walking and the perception of static images of actors in walking postures rely on common brain mechanisms that are primarily object centered, rather than viewer centered, and that are blind to the identity of the actor. These results, obtained with human psychophysical adaptation techniques, support previous evidence accumulated using single-unit recording in nonhuman primates. In addition, these results provide evidence that current models of human action recognition require an object-centered processing stage.     

Visual masking by light offset

Two experiments are reported which investigated whether or not the offset of light can serve as a backward masking stimulus (MS). In both studies, human Os made identification responses to graphemes (TS) presented tachistoscopically on a lighted field. Simultaneously with or at short intervals after TS offset, the lighted background field was shut off. The termination of the background field served as the MS. The results indicated a reliable masking effect due to light     

Visual imagery in backward masking

Observers viewed briefly presented target dot patterns, either at low contrast without a mask (no mask, or NM) or at high contrast and followed by a long-lasting patterned mask (backward masking, or BM). Experiment 1 demonstrated independent processing of NM target dots but limited capacity processing of BM target dots. Experiments 2 and 3 showed that visual images may radically change sensitivity (d′) in BM but not in NM. Results suggest that d′ is reduced if the image suppresses dots relevant for the detection task, but that d′ is raised if the image suppresses dots that compete for processing with those the observer must detect.     

Visual backward masking in retardates and normals

Educable adolescent male retardates were compared with normal males of equal CA and equal MA on a visual backward masking task. Significantly shorter interstimulus intervals were required to induce a masking effect in the equal-CA group than in the retarded and equal-MA groups, who did not differ from each other. Speed of visual processing is a function of MA. It is related to CA in normals. and to IQ when retardates are compared with equal-CA normals.     

Visual masking and carbon monoxide toxicity.

Thresholds for letters were measured with and without a masking stimulus (presented either to the same eye as the letters or to the other eye) before and after exposure of smokers and nonsmokers to 500 ppm carbon monoxide (CO) in air for 1 hr. Identification of the unmasked letters was not degraded by CO but a number of thresholds of the masked letters were significantly affected among the smokers. The effects of the CO on binocular and interocular masking were similar. These results suggest that the first effects of CO toxicity are neither on the receptors nor central but on the transmission lines in between and that smokers are more susceptible than nonsmokers to short-term increases in the level of CO. The masking phenomenon, however, does not appear to be an unusually sensitive measure of CO toxicity.     

Visual masking,mental age,and retardation

Performance of retarded subjects under both forward and backward masking was less accurate than either an equivalent chronological age or equivalent mental age group of normals. It was suggested that the iconic memory impairment of retarded subjects in attributable in part to mental retardation and not simply to low mental age.     

Vibrotactile masking: The role of response competition

When two tactile patterns, a target and a nontarget pattern, are presented in close temporal proximity to the same location, the nontarget pattern may interfere with the identification of the target. A series of experiments examined the extent to which the interference in target identification results from masking (interference in the representation of the target at an early stage of processing) or from response competition. A response competition view of pattern perception holds that both the target and nontarget are fully processed to the level of evoking responses. Interference is produced when subjects select the nontarget rather than the target. This view was tested with a paradigm developed in studies of selective attention. Pairs of tactile patterns were presented to subjects’ left index fingerpads. The amount of interference produced by a nontarget that is physically different from a target depends on whether the nontarget is associated with the same response as the target or a different response. The amount of masking also depends on the set of target and nontarget patterns that are used. The results support the conclusion that subjects have available a representation of both the target and the nontarget and that a substantial portion of the interference previously attributed to masking may be due to response competition.     

Visual perceptive simultaneity and masking of letters successively presented

Two sets of letters S₁ and S₂ when presented successively are perceived as simultaneous if the total duration of time from the beginning of S₁ to the end of S₂ is kert constant, whatever the duration of S₁, S₂, or the interval. The same law applies in the case of dots arranged to form geometrical figures. On the other hand, the phenomena of meta-contrast with letters are modified when the relative duration of S₁, S₂, and the interval vary. Thus perceptive integration and masking depend upon different processes.     

Visual perceptive simultaneity and masking of letters successively presented

Two sets of letters S₁ and S₂ when presented successively are perceived as simultaneous if the total duration of time from the beginning of S₁ to the end of S₂ is kert constant, whatever the duration of S₁, S₂, or the interval. The same law applies in the case of dots arranged to form geometrical figures. On the other hand, the phenomena of meta-contrast with letters are modified when the relative duration of S₁, S₂, and the interval vary. Thus perceptive integration and masking depend upon different processes.     

Visual processing of multielement arrays and selective backward masking

In the first of two selective masking experiments, 7-letter rows were followed at several ISIs by a mask or no-mask and a bar-marker partial report cue. The results suggest that the arrays were processed ends-first and then, in general, from both ends towards the middle. In the second experiment, bar-marker partial report cues were presented at the onset or offset of 6-letter/1-digit or 7-letter rows. The subjects could not anticipate the category of the to-be-reported item with the alphanumeric displays. With a delayed cue, selective masking was obtained with both mixed category and pure letter arrays, but with simultaneous cuing, masking was always distributed across all serial positions. The results suggest that the subjects: (a) abstracted some information about category from the mixed arrays during an initial parallel stage of processing, (b) selectively attended to mainly the cued item with simultaneous probes with homeogeneous and mixed category displays, and (c) employed an ends-first processing strategy with both types of arrays when the bar-marker partial report cue was delayed.     

Backward masking,disinhibition, and hypothesized neural networks

Backward masking, metacontrast, and disinhibition can be obtained under a variety of conditions. The mechanisms that underlie each depend, of course, upon the particular conditions responsible for the effects. Theoretical expositions seeking to explain phenomena produced by small brief concentric disks of light in the same terms as those necessary to explain effects produced by large displaced complex patterns of light are likely to be wrong.     

Visual masking plays two roles in the attentional blink

When two targets are displayed in rapid visual sequence and masked by trailing patterns, identification accuracy is nearly perfect for the first target but follows a U-shaped pattern over temporal lag for the second target. Three experiments examined the role of visual masking in this attentional blink. Experiment 1 compared integration and interruption masks for both targets. Although either mask was effective in producing the blink when applied to the first target, only the interruption mask was effective when applied to the second target. Experiment 2 showed that integration masking of the second target was ineffective over a wide range of accuracy levels. Combining the two forms of masking in Experiment 3 confirmed the dissociation: A combined mask and only a main effect on accuracy for the first target, whereas it produced a qualitatively different pattern over temporal lag for the second target. These results suggest that representations of the target are substituted in consciousness by that of the interruption mask when visual attention is preoccupied.     

Visual backward masking as measured by voice reaction time

Instead of using percent correct identifications or detections as the dependent variable, latency in voicing the target stimulus was measured in a backward masking paradigm. Reaction time (RT) to target letters was reliably increased when they were simultaneously encircled by a black ring mask of a size found to produce masking using an identification or detection criterion. The masking function in terms of RT was typical in shape, a decreasing function of stimulus onset asynchrony (SOA) over an interval of 150 msec. Since the target remained “on” when the mask appeared, the results are incompatible with an erasure interpretation of masking effects. Analyses of the variances of the RTs supported an interpretation of a progressive decrease in masking effects as SOA increased.     

Visual masking effects on duration,size, and form discrimination

In duration, size, and form discrimination tasks, a visual noise mask was presented at variable delays after stimulus offset in order to interrupt processing and control the extent of processing time. Previous work (Thomas & Cantor, 1975) had suggested that both perceived duration and perceived nontemporal “information” might be expected to increase as processing time was extended. As predicted, accuracy in the discrimination of size of circles and form of non-sense figures was found to vary directly with stimulus duration (20, 50 msec) and mask delay interval (0, 30, 70, 110 msec). Differences in perceived duration between filled (forms or circles) and unfilled (blank) intervals were found to increase monotonically with increases in the mask delay interval, when non-sense forms, but not circles, were presented. Two hypotheses of visual masking (“integration” and “interruption”) are discussed. Within the context of the “integration” hypothesis, a model is proposed which predicts processing time as a function of stimulus duration, mask delay interval, and the interval between onset of the mask and termination of processing.