Backward masking by pattern stimulus offset

The backward masking effects of the offset of a pattern stimulus on the apparent contrast of a target stimulus were determined to be a function of target onset-mask offset asynchrony. With spatially overlapping stimuli and binocular viewing, a monotonic function similar to that characterizing early dark adaptation was obtained; with a dichoptically presented disk onset as target and a surrounding ring offset as mask, a typical U-shaped metacontrast effect as a function of target onset-mask offset asynchrony was obtained. These mask-offset effects are related to the possible roles of (a) peripheral "off" mechanisms and (b) central metacontrast mechanisms in terminating visual response persistence in sustained channels.     

Backward masking interrupts spatial attention,slows downstream processing,and limits conscious perception

The attentional blink (AB) is a difficulty in correctly processing a target when it follows one or more other targets after a short delay. When no backward mask is presented after the last critical target, there is no or little behavioral AB deficit. The mask plays an important role in limiting conscious access to target information. In this electrophysiological study, we tested the impact of masking on the deployment and engagement of attention by measuring the N2pc and P3 components in an RSVP paradigm. We found that the presence of a mask in an AB paradigm reduced the amplitude of the N2pc, P3a, and P3b components. In addition to reducing encoding in memory, masking also reduced the effectiveness of the deployment and engagement of attention on the last target. We discuss the role of these findings in the context of current masking, consciousness, and AB models.     

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.     

Backward masking, the suffix effect, and preperceptual storage

This article considers the use of auditory backward recognition masking (ABRM) and stimulus suffix experiments as indexes of preperceptual auditory storage. In the first part of the article, two ABRM experiments that failed to demonstrate a mask disinhibition effect found previously in stimulus suffix experiments are reported. The failure to demonstrate mask disinhibition is inconsistent with an explanation of ABRM in terms of lateral inhibition. In the second part of the article, evidence is presented to support the conclusion that the suffix effect involves the contributions of later processing stages and does not provide an uncontaminated index of preperceptual storage. In contrast, it is claimed that ABRM experiments provide the most direct index of the temporal course of perceptual recognition. Partial-report tasks and other paradigms are also evaluated in terms of their contributions to an understanding of preperceptual auditory storage. Differences between interruption and integration masking are discussed along with the role of preperceptual auditory storage in speech perception.     

Audiovisual speech from emotionally expressive and lateralized faces

Emotional expression and how it is lateralized across the two sides of the face may influence how we detect audiovisual speech. To investigate how these components interact we conducted experiments comparing the perception of sentences expressed with happy, sad, and neutral emotions. In addition we isolated the facial asymmetries for affective and speech processing by independently testing the two sides of a talker's face. These asymmetrical differences were exaggerated using dynamic facial chimeras in which left- or right-face halves were paired with their mirror image during speech production. Results suggest that there are facial asymmetries in audiovisual speech such that the right side of the face and right-facial chimeras supported better speech perception than their left-face counterparts. Affective information was also found to be critical in that happy expressions tended to improve speech performance on both sides of the face relative to all other emotions, whereas sad emotions generally inhibited visual speech information, particularly from the left side of the face. The results suggest that approach information may facilitate visual and auditory speech detection.     

Comparing contrast-modulated and luminance-modulated masking: effects of spatial frequency and phase

The masking of a sinusoidal test grating by contrast-modulated (CM) gratings could, in principle, be attributable to the presence of a distortion product, injected into the stimulus during some nonlinear transformation at an early level of visual processing (e.g. Nachmias, 1989 Vision Research 29 137-142). If so, CM gratings and luminance-modulated (LM) gratings of similar effective contrast and spatial frequency should mask the detection of sinusoids in a similar fashion. We compared the effects of masking by 1 cycle deg-1 CM gratings [both simple beats (8 + 9 cycles deg-1) and amplitude-modulated gratings (8 + 9 + 10 cycles deg-1)], with those of masking by 1 cycle deg-1 LM gratings of low contrast. We found that: (i) CM and low-contrast LM grating masks yielded similar spatial-frequency tuning functions around the modulation frequency of 1 cycle deg-1; (ii) low-contrast LM gratings masked the detection of test sinusoids in a highly phase-dependent fashion, while masking by CM gratings did not vary systematically with relative spatial phase. The results suggest that masking produced by CM gratings cannot simply be explained by the presence of a distortion product at the beat or modulation frequency.     

Audiovisual speech from emotionally expressive and lateralized faces

Emotional expression and how it is lateralized across the two sides of the face may influence how we detect audiovisual speech. To investigate how these components interact we conducted experiments comparing the perception of sentences expressed with happy, sad, and neutral emotions. In addition we isolated the facial asymmetries for affective and speech processing by independently testing the two sides of a talker's face. These asymmetrical differences were exaggerated using dynamic facial chimeras in which left- or right-face halves were paired with their mirror image during speech production. Results suggest that there are facial asymmetries in audiovisual speech such that the right side of the face and right-facial chimeras supported better speech perception than their left-face counterparts. Affective information was also found to be critical in that happy expressions tended to improve speech performance on both sides of the face relative to all other emotions, whereas sad emotions generally inhibited visual speech information, particularly from the left side of the face. The results suggest that approach information may facilitate visual and auditory speech detection.     

The horizontal and vertical relations in upright faces are transmitted by different spatial frequency ranges

Faces convey distinct types of information: features and their spatial relations, which are differentially vulnerable to inversion. While inversion largely disrupts the processing of vertical spatial relations (e.g. eyes’ height), its effect is moderate for horizontal relations (e.g. interocular distance) and local feature properties. The SF ranges optimally transmitting horizontal and vertical face relations were here investigated to further address their functional role in face perception. Participants matched upright and inverted pairs of faces that differed at the level of local featural properties, horizontal relations in vertical relations. Irrespective of SF, the inversion effect was larger for vertical than horizontal and featural cues. Most interestingly, SF differentially influenced the processing of vertical, horizontal and featural cues in upright faces. Vertical relations were optimally processed in intermediate SF, which are known to carry useful information for face individuation. In contrast, horizontal relations were best conveyed by high SF, which are involved in the processing of local face properties. These findings not only confirm that horizontal and vertical relations play distinct functional roles in face perception, but they also further suggest a unique role of vertical relations in face individuation.     

Backward and forward masking associated with saccadic eye movement

Visual masking effects on test flash thresholds were measured under real and simulated eye movement conditions to determine whether visual masking is primarily responsible for elevations in threshold that are sometimes associated with saccadic eye movements. Brief luminous flashes presented to the central retina before, during, and after saccades were masked by stimuli presented either pre- or postsaccadically. The amount and time course of masking were quantitatively dependent on stimulus parameters of intensity and temporal separation and were unaffected by eye movement parameters (amplitude, velocity, direction) as long as retinal stimulus conditions were constant. The duration of forward masking was longer than that of backward masking. When retinal conditions during saccades were mimicked while the eyes were held steady, masking interactions were identical to those obtained during real saccades. These results indicate that masking effects during saccades in ordinary environments are determined solely by the stimulus situation at the retina. Putative nonvisual, centrally originating saccadic suppression suggested by other authors is evidently not additive with visually determined masking during saccades.     

Backward and forward masking in the perception of cutaneous stimuli

Masking of the perception of an electrical test stimulus by a mechanical shock was studied in six Ss. Forward and backward masking were observed in all Ss, the former being of longer duration. Duration of the masking effects is inversely related to the intensity of the test stimulus. Masking effects may be preceded and followed by perceptual facilitation. The masking effects may be responsible for the alterations in the perception of a somaesthetic stimulus before and during movement of the stimulated area.     

Asymmetry of masking between noise and tone

A pure tone was used to mask narrow and wide bands of noise centered on the frequency of the tone. In a given experimental session, the sound-pressure level (SPL) of the tone was held constant and loudness balances were obtained between a masked and unmasked noise band of equal width. These results are compared to earlier measures of the partial masking of tone by noise. The comparison shows that noise masks a tone more effectively than the tone masks the noise. Although the effect of the tone on a critical band of noise is greater than its effect on either an octave-band noise or wide-band noise, it is considerably smaller than the effect of the noise on the tone. Decreasing the noise bandwidth still further to a subcritical width reduces the asymmetry of masking somewhat, but a difference at high intensities of about 20 dB between the masking effects of an equally intense noise and tone remains. Whether the masker is a tone or noise, masking ceases when the effective energy of the masked and masking stimuli is the same.     

Effects of auditory masking by white noise on variability of fundamental frequency during highly similar productions of spontaneous speech

Six adults (3 men, 3 women) produced highly similar spontaneous speech utterances during quiet and 90-dB SPL white noise. Although subjects' fundamental frequency (fo) was significantly increased when speaking in noise, their fo variability (coefficients of variation) throughout the utterance was not affected by the auditory disruption. This indicated that their ability to vary fo for linguistic stressing was preserved under short-term disturbed auditory feedback. These findings further supported the hypothesis that fo is under open-loop regulation.     

The masking of octave-band noise by broad-spectrum noise: A comparison of infant and adult thresholds

Localization responses to a 4,000-Hz octave-band noise in a background of broad-spectrum noise were obtained from infants, 6, 12, 18, and 24 months of age, and adults. A two-alternative, forced-choice procedure was used to determine thresholds at each of two levels of masking noise, 42 and 60 dBC. Adults were also tested for their localization of pure tones in noise and their detection of octave-band noises with the more traditional two-interval, forced-choice task. Increasing the masking noise from 42 to 60 dBC resulted in comparable threshold shifts for all age groups. However, infant thresholds were 16–25 dB higher than those obtained for adults. The theoretical implications of these findings are discussed.