The relation of phenomenal brightness reversal and re-reversal to backward masking and recovery

Three recent experiments have demonstrated that a visual target suppressed through backward masking can be recovered by the introduction of a second mask. Present theories of backward masking cannot account for this since they assume that a masked target has no representation in the visual system. Amechanism is suggested to account for both visual backward masking and recovery in terms of lateral inhibition. Experimental evidenc e is offered in support of the hypothesized mechanism.     

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.     

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.     

Auditory forward and backward masking interaction

Recent research on forward masking and backward masking has led us to the hypothesis that combined forward and backward masking may involve at least two different types of interaction patterns. The previously documented interaction results in masking are greater than predicted by the simple summation of masking effects obtained with each masker alone (Lynn & Small, 1977; Patterson, 1971; Wilson & Carhart, 1971). Another possible type of interaction is based upon the finding that backward masking, but not forward masking, can be reduced by cues providing timing information (Puleo & Pastore, 1980). A forward masker appears to involve minimum temporal uncertainty (Pastore & Freda, 1980) and, therefore, should be able to act as such a source of timing information to reduce the contribution of a later occurring backward masker. Both types of interaction patterns were found, with the specific forward and backward masker parameters determining which pattern is observed.     

Temporal integration and vibrotactile backward masking

Subjects were presented with vibrotactile target patterns to their left index fingertips. The target patterns varied in the number of line segments that they contained and were presented in the presence or absence of a backward-masking stimulus. The stimulus onset asynchrony (SOA) between the target and masker was varied. In an identification task, subjects' errors indicated that the effect of the masker at brief SOAs was to increase the perceived number of line segments in the target. This effect diminished with increasing SOA, and at the longest SOAs subjects confused targets with patterns containing the same number of line segments but varying in how the line segments were related. In an estimation task, the effect of the masker was to increase the number of line segments estimated to be contained in the target pattern. The effect of the masker at brief SOAs is discussed in terms of an integration theory of vibrotactile backward masking. At longer SOAs, the results suggest that the masker may interfere with the extraction of relational information in the target pattern.     

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.     

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.     

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.     

Interaction of forward and backward visual masking

An investigation was conducted into the interaction of the forward and backward masking effects of unpatterned visual stimuli. It was found that detection of a test spot was easier under conditions that should have provided both forward and backward masking than under either forward masking or backward masking alone. The implications for an integration theory of masking are discussed, and the findings are contrasted with findings on the interaction of forward and backward masking by dynamic visual noise.     

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.     

Similarity effects in backward recognition masking

Auditory backward recognition masking refers to the ability of a masking sound to terminate further perceptual resolution of a test sound presented slightly earlier in time. The present experiments were conducted to determine whether mask/test tone similarity effects in backward recognition masking could be reliably demonstrated. Although similarity effects were found in Experiments 1 and 2, only about 60% of the subjects demonstrated these effects. Experiment 3 was designed to isolate which stage of information processing is responsible for similarity effects. It was hypothesized that similarity effects are due to mask interference with the synthesized auditory memory of the test tone rather than to selective overwriting of a preperceptual auditory store: previous research has shown that interference in synthesized auditory memory depends on the similarity of the interfering stimulus to the items held in memory. By independently varying the backward masking interval and the interfering effect of the mask on the test tone memory, it was possible to demonstrate that similarity effects are indeed caused by mask interference in synthesized memory. The implications of these results are considered in the framework of auditory and visual masking.     

Reaction time measures of backward masking

We employed both simple and choice reaction time (RT) paradigms in which the subjects were required to respond to 3.0 cycles per degree (c/d) square-wave gratings presented to one eye, while checkerboard masks were presented at various stimulus-onset asynchronies to the other eye. No masking was evident using the simple RT paradigm, but with the choice RT task, checkerboard masks presented to the contralateral eye of three subjects resulted in substantial decreases in response speed when the test preceded the mask by stimulus-onset asynchronies of 25 to 75 ms. Masks that contained lower fundamental spatial frequencies (1.0 c/d) than the target were more effective than masks containing fundamental spatial frequencies (6.0 c/d) higher than the target, while masks that contained fundamental components identical to those in the target (3.0 c/d) produced maximum masking. The results offer support for the sustained-transient theory of visual processing and validate RT as a technique for examining spatio-temporal factors in masking.     

Testing quantitative models of backward masking

We analyzed the relationship between U-shaped and monotonic-shaped masking functions, using both computer simulations of quantitative models and experimental data. Our analysis revealed that quantitative models of backward masking predict that U-shaped masking functions should appear for weak masks and monotonic masking functions should appear for strong masks. The models predict, moreover, that for a fixed target and experimental task, as the mask changes it is possible to go from U-shaped to monotonic-shaped masking functions. Significantly, the models predict that at each stimulus onset asynchrony between the target and the mask, the U-shaped function must have weaker masking than the monotonic-shaped function. Contrary to the predictions of the models, we show an experimental situation that generates masking functions that violate this prediction.     

Effect of backward masking onsame-different judgments

Subjects judged whether two adjacent letters were identical or different. The letter pair was presented briefly, followed by a superimposed patterned mask (Experiments 1 and 2) that was intended to terminate processing early. Previous work using variation in speed stress (Krueger & Chignell, 1985) had indicated that false-same errors (i.e., ondifferent pairs) predominate in early processing (missing-feature principle), whereas false-different errors predominate in late processing (internal-noise principle). The mask did not terminate processing early, however, because it produced a large preponderance of false-different errors (9%). Also, both response time (RT) and the standard deviation of RT increased as the stimulus-onset asynchrony between letter pair and mask decreased. The results indicate that backward masking works by integration (C. W. Eriksen, e.g., 1966) rather than by interruption (Sperling, 1963), and is a graded rather than all-or-none phenomenon. Consistent with the internal-noise principle, a lateral mask (Experiment 2) produced a large preponderance of false-different errors (7%) and a large fast-same effect (50 msec).     

Dichotic backward masking of complex sounds

In the first experiment subjects identified a consonant-vowel syllable presented dichotically with a known contralateral masking sound at a stimulus onset asynchrony of ± 60 msec. When the mask followed the target syllable, perception of place of articulation of the consonant was impaired more when the mask was a different consonant-vowel syllable than when it was either a steady-state vowel or a non-speech timbre. Perception was disturbed less when the mask preceded the target, and the amount of disruption was independent of which mask was used. Greater backward than forward masking was also found in the second experiment for the identification of complex sounds which differed in an initial change in pitch. These experiments suggest that the extraction of complex auditory features from a target can be disrupted by the subsequent contralateral presentation of a sound sharing certain features with the target.     

Spatial extent and figural factors in backward masking

Spatial and figural characteristics of backward masking were studied, with two collinear arcs presented end-to-end and serving as target and mask, respectively. Stimulus onset asynchrony was 50 ms while interstimulus interval was 0 ms. Mask exposure duration required for masking was determined as a function of target length with mask length as a parameter. The exposure duration of the mask required for complete masking varied directly with target length, but inversely with mask length. The fact that masking strength increased with mask duration while all other parameters were kept constant suggests that masking depended on stimulus termination asynchrony. Maximal masking occurred for target arcs as long as 5.0 deg of visual angle, exceeding previously reported distances. Misaligned or differently shaped stimuli produced less masking, suggesting that figural factors play a role in long-range backward masking.     

Individual brightness functions

A total of 34 individual brightness functions were measured for 18 observers by two different methods. In one method the observer set various luminance levels of a white target and assigned numbers proportional to the apparent brightness of the levels set. In the other method the observer adjusted the loudness of a white noise and the luminance of a white target in order to achieve a series of cross-modality matches between loudness and brightness. Both methods gave good approximations to power functions, showing that the psychophysical power law holds for the individual perceiver.