Backward Masking Paradigm Research Articles

Spatial Extent of Masking by Sine-Wave Gratings

The contrast threshold for detection of a target consisting of 1.5 periods of a sine wave was determined as a function of the number of cycles in a sinusoidal mask with the same spatial frequency and orientation. The test frequencies were 2, 4, and 8 cycles deg−1. The masks were spatial-frequency modulated so as to equate their spectral extent. Stimuli were seen monocularly in Maxwellian view at a mean luminance of 10 cd m−2. The contrast threshold in a backward masking paradigm was determined by a 2AFC staircase. Data were obtained from three subjects with normal vision. It was found that as the number of cycles in the mask was increased, the contrast threshold fell, but only to a certain level. The full range of the threshold decrement was about 2 dB. At all the spatial frequencies tested, the final threshold level was reached with 3 cycles in the mask and then remained unaffected by a further increase in the number of cycles. The results implicate frequency-tuned mechanisms of very restricted spatial extent. It is suggested that these may underlie processing of spatially distributed information at the post-striate stages.

Backward masking performance during and after manic episodes.

In a longitudinal design, 16 inpatients with bipolar mood disorder and 16 normal control participants were administered measures of backward masking. Bipolar inpatients were assessed while actively manic and again following manic episode. Clinical state was determined from ratings on an expanded version of the Brief Psychiatric Rating Scale. Two backward masking paradigms were used: (a) a staircase method, which yielded a critical interstimulus interval, and (b) set interstimulus intervals, which provided a masking function. Bipolar patients performed significantly worse than the normal controls at both sessions, but the Group X Session interaction was nonsignificant with both masking procedures. The masking performance deficit for the manic patients was not related to the presence of psychotic symptoms but seemed to be partially associated with lithium treatment. The results indicate that the impaired masking performance of manic patients is not strictly limited to the period of the manic episode.

Brain mechanisms for invariant visual recognition and learning

Mechanisms by which the brain could perform invariant recognition of objects including faces are addressed neurophysiologically, and then a computational model of how this could occur is described. Some neurons that respond primarily to faces are found in the macaque cortex in the anterior part of the superior temporal sulcus (in which region neurons are especially likely to be tuned to facial expression, and to face movement involved in gesture). They are also found more ventrally in the TE areas which form the inferior temporal gyrus. Here the neurons are more likely to have responses related to the identity of faces. These areas project on to the amygdala and orbitofrontal cortex, in which face-selective neurons are also found. Quantitative studies of the responses of the neurons that respond differently to the faces of different individuals show that information about the identity of the individual is represented by the responses of a population of neurons, that is, ensemble encoding is used. The rather distributed encoding (within the class faces) about identity in these sensory cortical regions has the advantages of maximising the information in the representation useful for discrimination between stimuli, generalisation, and graceful degradation. In contrast, the more sparse representations in structures such as the hippocampus may be useful to maximise the number of different memories stored. There is evidence that the responses of some of these neurons are altered by experience so that new stimuli become incorporated in the network, in only a few seconds of experience with a new stimulus. It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation. Thus the representation is in a form which is particularly useful for storage and as an output from the visual system. It is also shown that one of the representations which is built is view-in-variant, which is suitable for recognition and as an input to associative memory. Another is viewer-centered, which is appropriate for conveying information about gesture. It is shown that these computational processes operate rapidly, in that in a backward masking paradigm, 20–40 ms of neuronal activity in a cortical area is sufficient to support face recognition. In a clinical application of these findings, it is shown that humans with ventral frontal lobe damage have in some cases impairments in face and voice expression identification. These impairments are correlated with and may contribute to the problems some of these patients have in emotional and social behaviour. To help provide an understanding of how the invariant recognition described could be performed by the brain, a neuronal network model of processing in the ventral visual system is described. The model uses a multistage feed-forward architecture, and is able to learn invariant representations of objects including faces by use of a Hebbian synaptic modification rule which incorporates a short memory trace (0.5 s) of preceding activity to enable the network to learn the properties of objects which are spatio-temporally invariant over this time scale.

Information-processing abnormalities as neuropsychological vulnerability indicators for schizophrenia.

Studies of schizophrenic patients in psychotic and clinically remitted states and of biological relatives indicate that subtle anomalies in information processing may be critical components of neuropsychological vulnerability to schizophrenia. We describe a conception of possible abnormalities and several recent strategies to differentiate these possibilities. Within Continuous Performance Test conditions, varying the perceptual load vs. the active, working memory load yields a distinction between a stable vulnerability factor across clinical states and a potential mediating vulnerability factor. Specialized backward masking paradigms offer ways to separate two initial sensory-perceptual processes from attentional shifting processes. Top-down attentional influences on sensorimotor gating allow examination of the role of central executive processes in modulating early sensory processes. Initial results are discussed.

Information processing in gifted versus nongifted African American, Latino, Filipino, and White children: Speeded versus nonspeeded paradigms

One hundred and sixty children were evaluated in a battery of four information-processing tasks: inspection time (backward masking paradigm), reaction time, coincidence timing, and mental counters (working memory). Half of the children were certified as gifted in a case study analysis; half were selected from the nongifted program in the same school district. Within each group (gifted vs. nongifted), half were in second to third grade and half in fifth to sixth grade. Finally, for each of the two main factors (Giftedness and Grade), there were an equal number of children from four ethnic backgrounds: African American, Latino, Filipino, and White. There were large differences on all four information-processing tasks as a function of grade and membership in the gifted program. Correlational analyses revealed that measures of speed of processing, particularly inspection time, were the primary correlates of both IQ and membership in the gifted program. The correlation coefficient ( r = .44) between a summary composite of the information-processing tasks and scores on the Standard Raven Progressive Matrices (SPM) test was significant. In addition, a significant relationship ( r = .30) between coincidence timing and scores on the SPM was confirmed. Implications of these findings are discussed.

Masking of faces by facial and non-facial stimuli

Abstract A visual masking technique was used as a tool to study the recognition of well-known faces. Famous faces, but unknown masks were used. The visual relation between target and mask was varied; the effect was measured in terms of the thresholds for reports of “familiarity” and the ability to name the target. Three experiments are reported, all of which employed a backward-masking paradigm. The target and mask had equal display times, and there was no interstimulus interval. Significant masking was found with face masks but none from either object or noise masks. Intermediate levels of masking were found from faces that were inverted, jumbled, or had their inner features removed. The third experiment found that face masks that were similar to the targets had an effect equal to dissimilar ones. In all three experiments no interaction was found between the type of mask and the thresholds for the familiarity and naming criteria. The results are discussed in terms of information-processing models of face...

A connectionist model of visual-word recognition that accounts for interactions between mask size and word length

A connectionist model is described, which accounts for data showing a “mask appropriateness” effect in word and letter recognition. In a backward-masking paradigm, if the letter fragment masks that are used are of a similar size to the word or word fragment they are masking, performance is better than if the masks are longer or discontinuous (Jordan, 1990). The model simulates these effects by adding to the familiar architecture of the interactive activation model “length” units, which are stimulated whenever word units of a particular letter length are active, and “mask” units, which are stimulated by masks of particular sizes and in turn stimulate length units. Detailed predictions of the model are examined for both forward and backward masking, and are found to be in good accord with the data.

Automatic and pre-lexical computation of phonology in visual word identification

Abstract Two experiments were conducted to evaluate the hypothesis that identification of a visually presented word involves phonological information that is activated pre-lexically and automatically. A backward masking paradigm was used in which a word target was followed by a pseudoword mask, followed in turn by a non-linguistic pattern mask. The stimulus materials were Serbo-Croatian. The pseudoword mask could share all but one phoneme in common with the target, or none; moreover, it could be printed in the same alphabet as the target (e.g. both stimuli printed in Cyrillic), or in the other alphabet (e.g. target in Cyrillic, mask in Roman). Word targets were always lower case, and pseudoword masks were always upper case. It was assumed that where a mask shares phonological information with the target it can compensate for the interruption in processing by continuing the activation of the phoneme units activated by the target. Such an effect would be pre-lexical because the phoneme units activated by th...

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.

Visual information processing speed in hypnotized and nonhypnotized subjects.

Using a backward-masking paradigm with a bias-free and ceiling-free psychophysical task, we tested hypnotized and control subjects for speed of visual information processing. Approximately half of each group received visual imagery suggestions in an attempt to influence attention. Imagery produced no significant differential effect. Although an absence of a hypnotizability-performance relationship was in keeping with findings of a previous study, those subjects in the present study who performed under hypnosis were, as a group, significantly superior to the other subjects in speed of information processing.

Hypnotizability and speed of visual information processing.

Abstract Following the determination of the luminance threshold of each S, high and low hypnotizable Ss were tested for speed of information processing using a backward masking paradigm with a bias-free and ceiling-free psychophysical task. No significant relationship between hypnotizability as measured by the Stanford Hypnotic Susceptibility Scale, Form A (SHSS:A) of Weitzenhoffer and Hilgard (1959) and speed of information processing was observed. The order of administering SHSS:A, pre- or postthreshold task, was significantly related to luminance threshold. Results were compared to other studies wherein some evidence for a relationship between hypnotizability and speed of visual information processing had been offered.

The effects of visual backward masking on young children and adults

Kindergarten children and adults were compared to determine possible age differences in some basic effects of backward masking. With an overlapping pattern mask, most subjects in both age groups processed the target faster with continuous viewing of the target before mask onset as compared with an intervening interstimulus interval. With a non-overlapping pattern mask, performance conformed more to the additive rule, i.e., that target duration plus the interstimulus interval needed for accurate identification of a target followed by a mask equals a constant. Both age groups showed a similar increase in the target duration needed for evasion of masking as mask duration was increased up to an asymptote, after which further increases in mask duration did not necessitate increases in target duration. The extremely similar performance of very young children and adults in the experiments reported supports the notion that the mechanisms underlying backward masking are very similar in both age groups. Implications of the results for selection of parameters in developmental studies using backward masking paradigms are discussed.

Susceptibility to backward masking in schizophrenic patients with positive or negative symptoms.

The authors used the backward masking paradigm to compare visual information processing in schizophrenic patients with predominantly positive or predominantly negative symptoms. The results indicate significantly slower information processing in patients with negative symptoms.

An electrocortical investigation of word recognition in a backward masking paradigm

An electrocortical investigation of word recognition in a backward masking paradigm

Dichoptic backward masking of letters, words, and trigrams in old and young subjects.

Age differences in central visual processing were studied in 30 older adults (mean age 67.9 years) and in 30 young adults (mean age 19.8 years) using a dichoptic backward masking paradigm. Single letters, three-letter words, and consonant trigrams were used as target stimuli with a patterned masking stimulus. A significant age difference (p less than .001) was found in the interstimulus intervals necessary to escape the masking effect (ISIc) with older subjects requiring approximately 75 msec longer than the younger ones at each of three target durations. The effect of letters, words, and trigrams on ISIc for both young and old also yielded a significant difference (p = .01) with words most readily identified, letters intermediate, and trigrams requiring the longest processing time. Implications of these data with respect to previous studies and theoretical models are considered.

Nonsimultaneous masking and temporal summation in the parakeet (Melopsittacus undalatus)

Behavioral thresholds for a 15-ms probe tone were obtained for three parakeets in a backward, forward, and a combined forward and backward masking paradigm as a function of masker frequency. For all three paradigms, threshold improved dramatically (∼10 dB) when masker frequency was ±20 Hz of the probe frequency compared to the equal masker and probe frequency condition. In the region of the “tip” of the masking function the Q10 dB values were 140, 20, and 70 for the backward, forward, and combined backward and forward masking paradigms, respectively. The sharpness of tuning in the frequency region of the probe is considerably greater than that found for humans tested with the same stimuli. Probe threshold also varied as a function of masker level and masker duration for both forward and backward masking paradigms. Temporal summation data for short tones and noises are consistent with previous data obtained with longer signals. [Work supported by NIMH.]

Oculomotor Factors In Visual Perceptual Response Efficiency

The preprogramming of saccadic eye movements is examined by studying the pattern of oculomotor sequences while scanning a visual display. The effects of interference employing a backward masking paradigm on the oculomotor response as well as on position judgment and stimulus identification are examined. Data indicate that the motor programming of an ocular saccade is linked to the perceptual analysis of target position and cannot be set in motion with an impairment in perceptual localization.

Age-related Differences in Two Stages of Central Perceptual Processes: The Effects of Short Duration Targets and Criterion Differences

Two experiments investigated age differences in speed of central perceptual processes using a dichoptic backward masking paradigm. Twelve young (mean age = 19.6 years) and 12 old (mean age = 68.5 years) adults served as subjects. Exp. 1 examined age differences in speed of central perceptual processes using an ascending limits procedure and forced-choice responding to control for criterion differences. Target durations from 2 to 30 msec were used to further test the fit of young and elderly masking functions to the additive rule believed to describe masking which arises centrally (Turvey, 1973). Results from Exp. 1 showed a 33% slower speed of processing in the elderly sample. Furthermore, masking functions for both age groups fit the central rule across the wide range of target durations used. Exp. 2 examined the perceptual detectability of a 2- and 20-msec target at 7 stimulus onset asynchronies between target and masking stimuli using a forced-choice procedure. Subanalysis of two different components of the observed masking functions suggested the elderly sample was equally slow in completing both an early and late stage of central perceptual processing.

Speed of information processing in high and low susceptible subjects: a preliminary study.

Abstract A backward masking paradigm was employed to test die hypothesis that high hypnotic susceptible Ss are able to process information at a faster rate than low susceptible Ss. The critical interstimulus interval was determined for 8 high and 8 low susceptible Ss. A t-test analysis of the critical interstimulus intervals showed a significant difference between high and low susceptible Ss with the high susceptible Ss showing a lower critical interstimulus interval. Mean critical interstimulus intervals for die high (76 milliseconds) and low (98 milliseconds) susceptible groups suggested that the high susceptible Ss were an average of 22 milliseconds faster at processing information. Results were interpreted as being consistent with, and providing support for attentional theories of hypnosis.

Aetiological factors in dyslexia: III. Ocular-motor factors in visual perceptual response efficiency.

The study concerned the effects of induced interference employing a backward masking paradigm, on the processing of sensory information and on the formation of perceptual-motor responses in 20 dyslexic and 20 normal children. Results indicate that dyslexics do not exhibit impairment in perceptual localization.