Nonmonotone backward masking functions and brightness reversals

Increasing the target-field luminance aids detection for a simultaneously presented black target disc and a black masking annulus. At an intermediate interval separating the onset of the target from the mask, increasing the target-field luminance reduces target detection. This decrease in performance occurs with both temporal and spatial forced choice tasks. With a spatial forced choice, an observer's performance can fall below chance. We associate below-chance performance with a brightness reversal of the black target disc, such that the target disc appears brighter than its surround. The occurrence of brightness reversals follows from our model of the Broca-Sulzer effect, and nonmonotone masking functions result from a generalization of luminance summation.     

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.     

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.     

The effect of masker duration on forward and backward masking

Temporal masking of clicks by noise was investigated using forward and backward masking paradigms. Both the noise duration and the temporal separation, ΔT, between the click and noise were varied. For very brief ΔTs (100 microsec) and for very long ΔTs (100 msec), the duration of the masker did not greatly affect the click threshold. However, for intermediate ΔTs (3 msec), the threshold increased by as much as 44 dB as the noise duration increased from 0.1 to 100 msec. Temporal weighting functions, which describe the relative effectiveness of the noise as a function of ΔT, were computed from these data.     

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.     

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.     

On-line simulations of models for backward masking

Five simulations of quantitative models of visual backward masking are available on the Internet at http://www.psych.purdue.edu/~gfrancis/Publications/BackwardMasking/. The simulations can be run in a Web browser that supports the Java programming language. This article describes the motivation for making the simulations available and gives a brief introduction as to how the simulations are used. The source code is available on the Web page, and this article describes how the code is organized.     

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.     

Modeling spatial and temporal aspects of visual backward masking

Visual backward masking is a versatile tool for understanding principles and limitations of visual information processing in the human brain. However, the mechanisms underlying masking are still poorly understood. In the current contribution, the authors show that a structurally simple mathematical model can explain many spatial and temporal effects in visual masking, such as spatial layout effects on pattern masking and B-type masking. Specifically, the authors show that lateral excitation and inhibition on different length scales, in combination with the typical time scales, are capable of producing a rich, dynamic behavior that explains this multitude of masking phenomena in a single, biophysically motivated model.     

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.     

Testing models of object substitution with backward masking

A briefly presented visual target stimulus can be difficult to identify if shown in the context of a mask stimulus. There are several quantitative models that have been used to explain many different masking effects. Here, we look at modeling what has been called object substitution. We analyze four models and show that three of the models work with a common principle, whereas the fourth behaves quite differently. The three similar models have previously been used to explain many other aspects of visual masking, whereas the fourth model was designed exclusively to deal with object substitution masking effects. We identify an experimental test on the basis of which to choose between the models. The experimental results support the behavior of the fourth model.