Diotic and dichotic frequency recognition in a single-interval temporal interference procedure

The frequency discriminability of a 70-dB SPL, 20-msec test tone followed 5 msec later by an equally intense 500-msec, 800-Hz interference tone was studied in a single-interval procedure for one diotic condition and three dichotic conditions. The test tone (T) and interference tone (I) were presented the same to both ears (ToIo, diotic condition) and in three dichotic conditions: (1) the interference tone was presented to the right ear (R) and the test tone to the left ear (L) (T_LI_R), (2) the interference tone was presented the same to both ears and the test tone to one ear (TmIo), and (3) the interference tone was presented the same to both ears and the test tone to both ears with an interaural phase reversal (TπIo). The threshold value for test tone frequency discrimination in the diotic temporal interference condition was approximately six times greater than that obtained without an interference tone. The three dichotic temporal interference conditions yielded essentially equivalent threshold values which were approximately 2.4 times that obtained when the test tone was presented without an interference tone. Therefore, although never equaling interference-free conditions, dichotic test tone presentations can improve frequency recognition relative to diotic conditions at intensities well above threshold. It is postulated that this improvement may be due to the spatial separation of test and interfering tones, rather than to possible differences in diotic vs. dichotic subjective intensities. Dichotic-diotic frequency recognition differences did not occur when a 100-msec interval separated the test and interfering tone or when the interfering tone preceded the test tone.     

Simultaneous masking in a dichotic emotion detection task

The present study investigated the possible role of ceiling effects in producing laterality effects of small magnitude in dichotic emotion detection. Twenty two right-handed undergraduate students participated in the present experiment. They were required to detect the presence of a target emotion in the expressions tones of happiness, sadness, anger, and neutrality presented dichotically. Stimuli were adjusted to 70 dB and occurred simultaneously with a white noise mask that had an intensity of 65, 70, 80, or 85 dB. Results showed a left ear advantage (LEA) for the 65 dB mask and a right ear advantage for the 85 dB mask, but only after two testing sessions. The possible existence of a generalized right ear bias that might affect the observed LEA for non-verbal tasks is discussed. Alternative explanations and limitations of the present experiment are also presented.     

Perceptual masking: Peripheral vs central factors

Perceptual masking was studied under binocular and dichoptic conditions in order to separate peripheral and central interference effects. Under binocular conditions, when the test flash (TF) and the blanking flash (BF) fell on both retinas, both retroactive and proactive masking were demonstrated. Under dichoptic conditions, when the TF fell on one eye and the BF on the other eye, thus eliminating opportunity for intraretinal interference, there was partial retroactive perceptual masking and no proactive masking. These results suggest that binocular proactive masking is due to peripheral light adaptation, that binocular retroactive masking is due to both peripheral and central effects, and that dichoptic masking is due solely to central retrochiasmal interference. It is proposed that dichoptic retroactive perceptual masking affords a method of investigating central perception time, i.e., the time to consolidate a perceptual experience.     

Loss of wavelength selectivity in contour masking and aftereffect following dichoptic adaptation

Two experiments measured the apparent orientation (aftereffect) and the threshold for detection (masking) of a colored grating viewed by one eye after exposure to a colored grating to the same or the opposite eye (monoptic inspection) or after stimulation of one eye by color and the other eye by contours (dichoptic inspection). Under the monoptic condition, the color relationship between the inspection and test stimuli exerted control over the extent of aftereffect and masking when the two stimuli were viewed with the same eye, but not when they were seen with different eyes. Aftereffect and masking were nonselective to wavelength following dichoptic inspection, irrespective of whether the test stimulus was presented to the color-adapted or to the contour-adapted eye. The results support other claims that visual detectors with chromatic and spatial tuning have monocular specificity.     

Preparing dichotic tapes using a digital music synthesizer

Digital music synthesizers represent audio signals in the form of binary coded numbers. These binary coded numbers can be manipulated by the operator, thereby altering the audio signal in a variety of ways. The present article describes how these capabilities can be used to produce perfectly aligned dichotic tapes in which the stimulus items are matched on all extraneous (timbre, amplitude, duration) factors.     

Personality and hemisphere function: Two experiments using the dichotic shadowing technique

Two experiments using nonpsychiatric samples employed the auditory dichotic shadowing procedure to examine the relationship between psychotic predisposition or symptomatology and differential hemisphere performance. In experiment 1, right-handed Ss with high scores on the EPQ P-scale failed to show the normal right-ear preference for verbal material. This findings was not replicated in experiment 2, where there was a marginally significant tendency for right-handed Ss with high scores on the Schizotypy Scale (STA) to fail to show the normal right-ear preference. Different patterns of results were obtained for males and females in experiment 2. The results provide partial support for earlier studies on the relationship between schizotypy and differential hemisphere function. It is argued that the different patterns of means obtained in these and other studies in this area are best explained by a structural-dynamic model of hemisphere functioning.     

Consciousness and emotion: ERP modulation and attentive vs. pre-attentive elaboration of emotional facial expressions by backward masking

Facial stimulus processing is an important topic to explain how people comprehend affective disposition in others. The effect of attentive and pre-attentive elaboration of emotional facial expression was explored in the present research by using backward masking procedure. Specifically, unconscious mental process of emotion comprehension was analyzed: pictures presenting a happy, sad, angry, fearful, disgusted, surprised expressions were submitted to 21 subjects in both attentive and pre-attentive conditions and event-related potentials (ERPs) were registered in the two conditions. The two processes, attentive and pre-attentive, seem to be similar in their nature, since they are marked by analogous ERP deflections. In fact, two ERP effects were found, a positive (P300) deflection, maximally distributed on the parietal regions, and a negative (N200) deflection, more localized on the frontal sites. Nevertheless, some differences between the two conditions were found in terms of quantitative modulations of the two peaks. The N200 effect, ampler in attentive condition, may be considered such as an index of conscious processing of emotional faces, whereas the P3 (P3a) effect, higher in pre-attentive condition, was considered a specific marker of the automatic, unconscious process during the emotional face comprehension.     

Order information in dichotic memory.

Three experiments were performed using a recognition probe procedure to test the subject's recognition of the order of two items from a dichotically presented list. In all three experiments subjects were unable to recognize simultaneous items as having been simultaneous unless the critical pair was the last pair in the list. In contrast, they were able to identify the order of items not originally presented simultaneously at better than a chance level. Performance did not differ as a function of whether the two critical items were presented to the same or different ears. The data were interpreted as indicating that subjects divide attention between competing inputs in the dichotic memory task and that the eary-by-ear order of report is a result of the format in which the items are stored.     

Frequency selectivity for hearing-impaired and broadband-noise-masked normal listeners

When evaluating frequency selectivity, it is difficult to determine if the deviation from normal performance observed for hearing-impaired listeners reflects abnormal cochlear function or normal, level-dependent changes in frequency selectivity. This experiment was designed to investigate the dependence of frequency-selectivity measures on threshold and signal level. Auditory-filter characteristics, critical ratios, forward-masked psychophysical tuning curves, and narrowband-noise masking patterns were obtained from normal-hearing listeners in quiet and in the presence of broadband noise at five levels. These findings were then compared to previously obtained frequency-selectivity measurements for subjects with mild-to-moderate sensorineural hearing loss whose absolute thresholds are comparable to the normal-hearing listeners' masked thresholds. The results suggest that frequency selectivity deterioriates as threshold increases for all subjects. However, the poor frequency selectivity exhibited by hearing-impaired listeners may not be explained entirely by the effects of threshold and signal level. Nevertheless, because frequency selectivity is poorer in the normal auditory system at higher stimulus levels, the deviation from normal performance observed for hearing-impaired listeners may not be as large as previously suggested.     

Variations in backward masking with different masking stimuli: I. Local interaction versus attentional switch

The types of stimuli used as targets and masks considerably change the masking functions in a way that requires us to abandon any single mechanism of masking as the sole explanation of backward masking. In the first of two reports in which the problem of the mask-dependence of masking is addressed, we explore the role of the relative spatial positioning of targets and masks in order to differentiate between local interaction and attentional models. If single letters were masked by double-letter masks then the relative spatial arrangement of the letters, which was changed in order to vary the involvement of metacontrast-like processes, had an effect at shorter SOAs, but not at longer SOAs where strong masking still persisted. This poses difficulties for proposing local contour interaction as the main mechanism of masking. Similarly, crowding effects alone cannot explain the results. Backward masking also involves attention being directed to working-memory processing of the succeeding object while abandoning the preceding object.     

Auditory attentional blink: masking the second target is necessary, delayed masking is sufficient.

When two target items (T1 and T2) are presented in rapid succession among fillers, processing T2 is often impaired. This phenomenon is known as the attentional blink (AB). Within the visual modality, this second-target deficit generally occurs only if T2 is masked by a trailing item. The current study was designed to examine whether masking of T2 also plays a critical role in the auditory AB. Results showed a reliable AB effect even when the item following T2 was replaced by silence. However, the AB deficit was abolished when T2 was the last presented stimulus. Our results suggest that, as in vision, T2 masking is necessary for the AB to take place in audition, but that masking is effective even when delayed, providing evidence that the phenomenon shares some functional mechanisms across sensory modalities.     

A comparison of upper vs. lower and right vs. left visual fields using lexical decision

A series of experiments using the lexical decision task was conducted in order to investigate the functional differences between the upper and lower visual fields (UVF, LoVF) in word recognition. Word-nonword discrimination was swifter and more accurate for word stimuli presented in the UVF. Changing the eccentricity did not affect the UVF advantage over the LoVF. UVF superiority over LoVF was found to be equivalent for both right and left visual hemifield (RVF, LVF). In general, presenting related word primes enhanced all visual field differences in a similar manner (UVF over LoVF and RVF over LVF). However, primes consisting of semantically constraining sentences enhanced the RVF advantage over the LVF, but did not affect the UVF and LoVF differentially. The argument is made that UVF superiority cannot be due to perceptual or attentional differences alone, but must also reflect top-down information flow.     

Sources of auditory masking in infants: distraction effects.

Previous work has demonstrated that infants' thresholds for a pure tone are elevated by a masker more than would be predicted from their critical bandwidths. The present studies explored the nature of this additional masking. In Experiment 1, detection thresholds of 6-month-old infants and of adults for a 1-kHz tone were estimated under three conditions: in quiet, in the presence of a 4- to 10-kHz bandpass noise at 40 dB SPL, and in the presence of the same noise at 50 dB SPL. The noise was gated on at the beginning of each trial. Adult thresholds were the same in all three conditions, indicating that little or no sensory masking took place in the presence of the noise. Infant thresholds were about 10 dB higher in the presence of the noise. We term this effect distraction masking. In Experiment 2, the effect of gating the noise on at trial onset was examined. Thresholds for the same tone were estimated in quiet and in the presence of the band-pass noise at 40 dB SPL, but the noise was presented continuously during the session. Under these conditions, distraction masking was still observed for infants. These findings suggest that a masker can have nonsensory effects on infants' performance in a psychoacoustic task.     

Informational masking and auditory attention.

Informational masking is broadly defined as a degradation of auditory detection or discrimination of a signal embedded in a context of other similar sounds; it is not related to energetic masking caused by physical interactions between signal and masker. In this paper, we report a systematic release from informational masking of a target tone in a nine-tone rapid auditory sequence as the target is increasingly isolated in frequency or intensity from the remaining sequence components. Improved target-tone frequency difference limens as isolation increases are interpreted as a reflection of increasingly focused auditory attention. The change from diffuse to highly focused attention is gradual over the frequency and intensity ranges examined, with each 1-dB increment in target intensity relative to the remaining components producing performance improvements equivalent to those produced by a 2% increase in frequency isolation. The results are modeled as bands of attention in the frequency and intensity domains. For attention directed by frequency isolation, there is a strong correspondence with auditory filters predicted by the power spectrum model of masking. These data also support the existence of an attention band of intensity, with a bandwidth of about 5-7 dB at the moderate levels used in this experiment.     

Hemispheric emotional asymmetry in a dichotic listening task.

In a dichotic listening experiment white noise was played to one ear and either music or poetry to the other ear. Subjects rated the stimuli on each of three dimensions. The results showed that both music poetry were judged as more pleasant when heard at the left than the right ear. In addition the music, but not the poetry, was perceived as more soothing at the left ear. The findings are discussed in relation to other indications in the literature that left and right cerebral hemispheres differ in their emotional make-up.