Lateral masking in visual information processing

When unrelated letter strings are presented tachistoscopically, the end letters are reported more often than their neighbors; and when spaces are inserted into strings, performance on certain adjacent letters is superior to performance on those letters when no spaces were present. An experiment was conducted to determine the nature of those spacing effects. Letter strings were presented at a variety of retinal locations, and spaces were inserted into different positions in the instructed left-right processing order. The space effect was unrelated to processing order, but it was dependent on retinal location. To account for the various asymmetries, it was necessary to postulate that letters tend to interact with adjacent lettersand that the interaction was not spatially symmetric. Furthermore, it was found that spaces had greater effects on “right-hand” letters than on symmetric letters. It was therefore concluded that letters interact at the feature level.     

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.     

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.     

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.     

Developmental change in visual information processing under backward masking

Four-year-olds, eight-year-olds, and college students were compared with respect to their speed and strategy for processing form information in a pointing-recognition task. The target form arrays, varying in size from one to four forms, were presented tachistoscopically, followed by a masking array at varying intervals. No age differences in processing speed were found on single-item arrays, but four-year-olds were progressively slower as array size increased. A selective processing condition resulted in longer processing times for all Ss but was differentially more difficult for four-year-olds. Under the full report conditions, all Ss showed a parallel independent processing strategy as array size increased from one to two items, but four-year-olds did not apply this strategy as efficiently as older Ss. As array size increased from two to four items, only adults and eight-year-olds continued to show parallel independent processing, up to a limit. This age difference in processing strategv for the largest arrays may underlie age differences that have been found in short-term memory capacity.     

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.     

Age effects in backward visual masking (Crawford paradigm)

Fifteen Ss in each of four age groups (5-, 10-, 16-, and 22–23-years old) received backward visual masking. Group effects occurred at longer ISIs indicating slower prerecognition processing for younger Ss. In a second experiment 19-, 35-, and 55-year-old Ss were administered backward visual masking under the identical procedures of Exp. 1. The oldest Ss performed significantly worse than 19- and 35-year-old Ss, which did not differ significantly from each other. The general methodological features of both studies, as well as the obtained relationships were discussed.     

Integration,interruption and processing rate in visual backward masking

Summary The identification of a briefly presented test stimulus is impaired when the test stimulus is followed by a masking stimulus consisting of random contours. Two theories have been proposed to account for this effect (backward masking by visual noise). According to interruption theory, the time which is available for test stimulus processing is limited by the onset of the masking stimulus. According to integration theory, test stimulus and masking stimulus are combined in a single percept where the test stimulus is degraded by the contours of the masking stimulus. A review of the methods used to decide between the two theories permits the conclusion that backward masking by visual noise requires a two-factor theory: integration for short (less than about 100 msec) and interruption for long test stimulus-masking stimulus asynchronies. It is shown that evidence for interruption can only be obtained when processing load is used as a converging operation. Finally, some approaches to the measurement of processing rate under backward masking are discussed.

---

Zusammenfassung Die Identifizierbarkeit eines tachistoskopisch dargebotenen Testreizes wird durch nachfolgende Exposition eines aus Zufallskonturen bestehenden Maskierreizes beeinträchtigt. Zur Erklärung dieser Maskierung durch visuelles Rauschen wurden zwei Theorien formuliert. Gemäß der Unterbrechungstheorie wird die zur Verarbeitung des Testreizes verfügbare Zeit durch die Darbietung des Maskierreizes verkürzt; gemäß der Integrationstheorie werden Test- und Maskierreiz in eine gemeinsame zentrale Repräsentation verwandelt, in der das Testreizäquivalent von den Maskierreizkonturen überlagert wird und dadurch eine Qualitätsminderung (degradation) erfährt. Die zur Entscheidung zwischen den beiden Theorien verwendeten Methoden werden analysiert, mit dem Ergebnis, daß die Maskierung durch visuelles Rauschen eine Zwei-Faktorentheorie erfordert: Integration für kurze (kleiner als ca. 100 msec) und Unterbrechung für lange Testreiz-Maskierreizintervalle. Es wird gezeigt, daß Unterbrechungseffekte nur dann nachgewiesen werden können, wenn die Belastung des informationsverarbeitenden Systems (processing load) als konvergierende Operation eingeführt wird. Schließlich werden Ansätze zur Messung der Geschwindigkeit der Informationsverarbeitung unter Maskierungsbedingungen referiert.

---

---

Preparation of this report was facilitated by International Postdoctoral Research Fellowship No. F05-TW-1794 from the Public Health Service, National Institutes of Health, Bethesda, Md., USA. The helpful remarks of Dr. A. O. Dick are appreciated.     

Integration,interruption and processing rate in visual backward masking

Summary In order to decide between the integration and the interruption theory of backward masking, an experiment is conducted where a cue stimulus preceding the test stimulus by various intervals requires either identification of one test stimulus item (partial report) or recall of the whole test stimulus (full report). In addition, the test stimulus-masking stimulus agynchrony and the luminance of the masking stimulus are varied. When identification accuracy is plotted as a function of cue stimulus-test stimulus interval, the partial-report data can be broken down in two segments: an asymptotic value for long (greater than 500 msec) and a region of decreasing accuracy for short cue stimulus-test stimulus intervals. The asymptotic value depends on the test stimulus-masking stimulus asynchrony and the luminance of the masking stimulus; however, the decrease of accuracy is not affected by these parameters when the scores are normalized with respect to upper and lower limits of performance. Full-report performance shows a uniform decrease across the whole range of cue stimulus-test stimulus intervals. The manner in which asymptotic values depend on the test stimulus-masking stimulus asynchrony and on masking stimulus luminance is taken as evidence of a two-factor theory of backward masking proposed in a previous paper (Scheerer, 1973). But the data on decrease of accuracy require a revision of this theory: under certain conditions, test stimulus degradation may be compatible with an interruption theory. The different temporal course of partial and full report accuracy is used to distinguish between a peripheral (eye movement-mediated) and a central component in critical item selection.

---

Zusammenfassung Zur Entscheidung zwischen der Unterbrechungs- und der Integrationstheorie der visuellen Maskierung wird ein Experiment durchgeführt, in dem ein in verschiedenen Abständen vor dem maskierten Testreiz dargebotener Indikatorreiz entweder zur selektiven Identifikation eines Testreizelements (Teilbericht) oder zur Reproduktion des gesamten Testreizes (Gesamtbericht) auffordert. Außerdem werden das Testreiz-Maskierreizintervall und die Leuchtdichte des Maskierreizes variiert. Wenn die Identifikationsgenauigkeit als Funktion des Indikator-Testreizintervalles aufgetragen wird, zerfallen die Teilberichtskurven in einen asymptotischen Wert für lange (größer als 500 msec) und in einen Bereich abfallender Genauigkeit für kurze Indikator-Testreizintervalle. Der asymptotische Wert hängt vom Testreiz-Maskierreizintervall und von der Leuchtdichte des Maskierreizes ab; im Bereich abfallender Genauigkeit sind die Kurven von diesen Parametern unabhängig, wenn sie hinsichtlich oberer und unterer Grenzwerte der Genauigkeit normalisiert werden. Die Gesamtberichtskurven zeigen einen gleichmäßigen Genauigkeitsabfall über den gesamten Bereich von Indikator-Testreizintervallen. Die Abhängigkeit des asymptotischen Werts vom Testreiz-Maskierreizintervall und von der Maskierreiz-Leuchtdichte wird als Hinweis auf die Gültigkeit der im Literaturbericht (Scheerer, 1973) formulierten Zwei-Faktorentheorie der visuellen Maskierung interpretiert. Jedoch erfordern die Befunde zum Abfall der Identiflkationsleistung eine Revision dieses Konzepts; unter bestimmten Bedingungen kann eine unterbrechende Wirkung des Maskierreizes zu einer Qualitätsminderung des Testreiz-Äquivalents führen. Aus dem unterschiedlichen Verlauf von Teilbericht und Gesamtbericht wird geschlossen, daß die Selektion eines Testreizelements in einen peripheren (durch Fixationsänderung vermittelten) und in einen zentralen Anteil zerlegt werden kann.

---

---

Preparation of this report was facilitated by International Postdoctoral Fellowship No. F05-TW-1794 from the Public Health Service, National Institutes of Health, Bethesda, Md., USA, and by Grant NIMH MH-10753 to Dr. Ralph N. Haber.     

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.     

Orthographic and phonological computation in visual word recognition: Evidence from backward masking in Hebrew

We employed the backward masking paradigm to map the early computation involved in the perception of printed words in Hebrew. By independently manipulating orthographic and phonological overlap between targets and masks, we examined whether orthographic and phonological structure imposes late or early constraints on lexical access. The results demonstrated that the probability of reinstating a masked target depended on both the orthographic and the phonological overlap between the target and the mask. However, whereas phonemic structure seems to constrain lexical access only at short exposure durations, orthographic overlap also exerts its influence at longer durations.     

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.     

The crossmodal facilitation of visual object representations by sound: evidence from the backward masking paradigm

We report a series of experiments designed to demonstrate that the presentation of a sound can facilitate the identification of a concomitantly presented visual target letter in the backward masking paradigm. Two visual letters, serving as the target and its mask, were presented successively at various interstimulus intervals (ISIs). The results demonstrate that the crossmodal facilitation of participants' visual identification performance elicited by the presentation of a simultaneous sound occurs over a very narrow range of ISIs. This critical time-window lies just beyond the interval needed for participants to differentiate the target and mask as constituting two distinct perceptual events (Experiment 1) and can be dissociated from any facilitation elicited by making the visual target physically brighter (Experiment 2). When the sound is presented at the same time as the mask, a facilitatory, rather than an inhibitory effect on visual target identification performance is still observed (Experiment 3). We further demonstrate that the crossmodal facilitation of the visual target by the sound depends on the establishment of a reliable temporally coincident relationship between the two stimuli (Experiment 4); however, by contrast, spatial coincidence is not necessary (Experiment 5). We suggest that when visual and auditory stimuli are always presented synchronously, a better-consolidated object representation is likely to be constructed (than that resulting from unimodal visual stimulation).