Frequency selectivity using tonal-temporal masking: Diotic vs. dichotic masking

A combined forward-backward masking procedure was used to investigate the threshold of a 30-msec, 500-Hz signal as a function of masker frequency. The signal thresholds were obtained in two signal conditions, diotic (So) and dichotic (S_π), and for two different temporal separations of the maskers. The maskers were 500 msec in duration and were presented at 75 dB SPL. The function relating masked signal threshold to masker frequency was used to describe frequency selectivity in the four conditions. There were no differences in frequency selectivity measured between the diotic and dichotic signal conditions and only a small difference measured between the two intermasker interval conditions. The S_π conditions yielded lower thresholds than did the So conditions. The change in intermasker interval from 10 to 50 msec lowered the threshold maximally 18 dB for the So condition and 13 dB for the S_π condition. The results indicate that in this tonal temporal masking procedure there are no differences between the diotic and dichotic critical bands.     

Frequency recognition in temporal interference tasks: A comparison among four psychophysical procedures

The frequency discrimination of a 20-msec test tone was measured for the same subjects in four psychophysical paradigms: a single-interval procedure, a two-alternative forced-choice procedure, a same-different procedure, and a method-of-adjustment procedure. In each paradigm, the 20-msec test tone was preceded or followed by a 500-msec, 800-Hz interfering tone. The interfering tone occurred 50 or 5 msec before the onset of the test tone (forward interference) or 100 or 5 msec after the offset of the test tone (backward interference). In each of the four paradigms and for each of the interference conditions the value of Δf for the test tone was varied symetrically around 800 Hz to obtain an estimate of the frequency discrimination thresholds. In all psychophysical paradigms except for the single-interval procedure, there were small or no significant differences in observers’ frequency discrimination behavior among the interference conditions. The thresholds for Δf from these conditions were approximately the same as those obtained without an interfering tone. In the single-interval task, when the test tone preceded the interfering tone (backward interference) by 5 msec, an increase in the value of Δf required for discrimination over that required in the other conditions was measured. These results suggest that the effect of backward interference on a target tone does depend on psychophysical procedure.     

The role of tone duration in dichotic temporal order judgment

Over the past two decades, a number of studies have been based on the dichotic temporal order judgment (TOJ) paradigm, to compare auditory temporal processing in various subpopulations to that of young, normal controls. The reported estimates of dichotic TOJ thresholds, expressed as the interstimulus intervals (ISIs) for 75 % accuracy among the controls, have varied. In the present study, we examined the influence of tone duration, within the 10- to 40-msec range, on dichotic TOJ accuracy and threshold. The results indicated that increases in either ISI or tone duration increased dichotic TOJ accuracy similarly, implying that changes in tone duration may affect dichotic TOJs simply by adding to the delay between onset of the tone at the lead ear and onset of the tone at the lag ear. The dichotic TOJ thresholds from three published studies that had used tones as stimuli and the dichotic thresholds from the present study all fell within 0.5 standard deviations from the theoretical line of a 10-msec reduction in threshold for every 10-msec increase in tone duration. When the dichotic TOJ threshold data from the present study and from the published studies were converted to stimulus onset asynchronies (SOAs) and plotted as a function of tone duration, they fell very close to or on a zero-slope line, indicating that when ISI and duration are summed to yield an SOA, dichotic TOJ thresholds are invariant to tone duration within the range of 10–40 msec.     

Signal detectability in the presence of monotic or dichotic noise bands of equal or unequal levels

The application of the power-spectrum model of masking to the detectability of a signal masked by dichotic noise was investigated in three experiments. In each experiment, the signal was a 2-kHz sinusoid of 400-msec duration, masked by either one or two 800-Hz wide bands of noise presented singly or in pairs. In Experiment 1, we compared the detectability of a diotic signal masked by dichotic noise with the detectability of a monaural signal masked by each of the noises separately. The spectrum level of the noise was 35 dB SPL. For dichotic presentations, the signal was sent to both ears while pairs of noise bands, one below and one above the signal frequency, were presented together, one band to each ear. Threshold levels with the dichotic stimuli were lower than or equal to the thresholds with either ear's stimulus on its own. Similar dichotic stimuli were used in Experiment 2, except that the signal frequency was nearer to one or the other of the bands of masking noise, and the noise had a spectrum level of 50 dB SPL. In Experiment 3, thresholds were obtained with two sets of symmetrically and asymmetrically placed notched-noise maskers. For one of these sets, the spectrum level of both noise bands was 35 dB SPL; for the other set, interaural intensity differences were introduced in the form of an inequality in the levels of the noise bands on either side of the signal. In one ear, the spectrum level of the lower frequency noise band was 35 dB SPL and the spectrum level of the higher frequency noise band was 25 dB SPL, whereas in the other ear, the allocation of noise level to noise band was reversed. The dichotic thresholds obtained with the unequal noise maskers could be predicted from the shapes of the auditory filters derived with equal noise maskers. The data from all three experiments suggest that threshold signal levels in the presence of interaural differences in masker intensity depend principally on the ear with the higher signal-to-masker ratio at the output of its auditory filter, a finding consistent with the power-spectrum model of masking.     

Pure-tone perception and ear advantages in dichotic listening

A same-different matching task was used to investigate how subjects perceived a dichotic pair of pure tones. Pairs of stimulus tones in four frequency ranges (center frequencies of 400–1,700 Hz), with separations between 40 and 400 Hzt were tested. Five types of test tones were matched to the stimulus pair: the stimulus pair presented again (control) or crossed over (same tones, different ears), the geometric mean of the two tones, or a binaural tone of the low or high tone of the pair. In the lowest frequency range and the highest with maximum separation, the crossed-over test tones were perceived as different from the same stimulus tones. A bias for perceiving the higher tone of a pair was evident in the frequency ranges with separations of 40-200 Hz. In the lowest frequency range, the bias was for perceiving the higher tone in the right ear. This restricted ear advantage in the perception of pure tones was not significantly related to the right-ear advantage in dichotic word monitoring.     

Tone-on-tone binaural masking with an antiphasic masker

One pure tone (500 Hz) was used to mask another pure tone of the same frequency and duration. The signal and masker were presented in three binaural stimulus configurations, Mo-So, Mo-Sπ, and Mπ -So. The Mo-So condition is a diotic condition; the Mo-Sβ condition is a dichotic condition in which the masker is homophasic and the signal is antiphasic; and the Mπ-So condition is a dichotic condition in which the masker is antiphasic and the signal homophasic. The signal-to-masker ratio required for detection was measured in each condition as a function of the signal-plus-masker phase angle, α. The data showed that the difference in detection between the Mo-Sπ and Mπ-So conditions varied between 0 dB when α=0 deg and 11 dB when α=90 deg. The difference in detection between the Mo-Sπ and Mπ-So conditions is due to the Os’ sensitivities to the interaural phase difference present in the Mo-Sπ and Mπ-So conditions. The results are similar to those obtained in investigations involving lateralization. The difference between detection in either the Mo-Sπ or Mπ-So condition and that in the Mo-So condition (the MLD) was variable due to differences in the Os’ sensitivities in the Mo-So condition.     

The bilingual-dichotic method for learning a foreign-language vocabulary

The bilingual-dichotic method organizes native and foreign words in paired-associate learning for optimum compatibility with study behaviour and asymmetric cerebral hemispheric specialization. Slow-paced auditory presentations alternate dichotic (simultaneous, native word at left ear and foreign word at right ear) and diotic (foreign word at both ears) input while the student views the word list in parallel to the dichotic format (native word-foreign word). More college students attained the criterion of perfect cuedrecall and in significantly less study time using the bilingual-dichotic method to learn English-Russian word pairs compared with those using the conventional (diotic Russian) or a reversed-ear dichotic control method. The new method yielded superior overall performance with significantly more accurate recall of the Russian words, and with shorter latencies of response than that obtained with the conventional method. Analysis suggests the bilingual-dichotic method combines attentional strategies with the right-ear advantage for dichotic verbal material to enhance rehearsal processes of learning. Practical applications of this new method for learning foreign vocabulary may be found in the early stages of foreign-language learning in coordination with other exercises.     

Dichotic, diotic, and monaural summation of loudness: a comprehensive analysis of composition and psychophysical functions

In a series of six experiments, the method of magnitude estimation, constrained by a multivariate model, was used to assess the rules that govern the summation of the loudness of two-tone complexes. This methodology enabled us to specify the amounts of summation and simultaneously to construct the corresponding loudness scales. The components had different frequency separations and in the different experiments were presented (1) dichotically, a different frequency to each ear; (2) diotically, to both ears; and (3) monaurally. Results replicated and in some conditions extended known features of multiple signal processing by the auditory system. Thus, qualitatively different rules of loudness integration appeared. For monaural and diotic modes of stimulation, overall loudness depended on total sound energy within the critical band, but on the simple sum of component loudnesses beyond the critical band. For dichotic presentations, a fully additive rule of loudness summation appeared, regardless of frequency spacing. For the latter (but not the former), loudness summation was perfect, with the underlying loudness scales closely approximating Stevens's sone scale.     

Contralateral interference and ear advantages for identification of three-element patterns

Recent experience with attempts to test relatively simple patterns such as three-tone sequences in a traditional dichotic-listening paradigm indicates that when such sequences are used for both target and contralateral interference, performance tends to be low in both ears and not useful for measuring or comparing ear advantages in various target conditions. It is reported that tests with a variety of sounds presented contralaterally to three-element patterns show that several such sounds can (1) allow performance in at least one ear to remain above floor values, (2) result in performance in at least one ear that is below ceiling, and (3) reveal ear advantages that are similar in direction and magnitude to those seen with the traditional dichotic paradigm.     

Sex differences in performance and hemispheric organization for a nonverbal auditory task

Musically experienced and inexperienced men and women discriminated among fundamental-frequency contours presented either binaurally (i.e., same contour to both ears) or dichotically (i.e., different contours to each ear). On two separate occasions, males made significantly fewer errors than did females in the binaural condition, but not in the dichotic condition. Subjects with prior musical experience were superior to musically naive subjects in both conditions. The dichotic pitch task produced a left-ear advantage, which was unrelated to gender or musical experience. The results suggest that the male advantage on the binaural task reflects a sex difference in the coordination of the two hemispheres during conjoint processing of the same stimuli rather than a difference in the direction or degree of hemispheric specialization for these stimuli.     

Sex differences in performance and hemispheric organization for a nonverbal auditory task.

Musically experienced and inexperienced men and women discriminated among fundamental-frequency contours presented either binaurally (i.e., same contour to both ears) or dichotically (i.e., different contours to each ear). On two separate occasions, males made significantly fewer errors than did females in the binaural condition, but not in the dichotic condition. Subjects with prior musical experience were superior to musically naive subjects in both conditions. The dichotic pitch task produced a left-ear advantage, which was unrelated to gender or musical experience. The results suggest that the male advantage on the binaural task reflects a sex difference in the coordination of the two hemispheres during conjoint processing of the same stimuli rather than a difference in the direction or degree of hemispheric specialization for these stimuli.     

Critical-band effects in two-channel auditory signal detection

Two-channel auditory signal detection was investigated with 50-msec sinusoidal signals masked by binaurally uncorrelated noise. In the two-channel tasks, the signals in each earphone channel were presented with an independent probability during the single observation interval and the observers were required to detect the inputs in a single earphone (selective-attention condition) or in both earphones (divided-attention condition). When the signals in each earphone were within the same critical band (the assumed singled processing unit in frequency domain), there was a decrement in detection performance in both the selective- and divided-attention (i.e. dichotic) conditions compared with the monaural condition. However, when signals were separated in frequency by several critical bands, a decrement in dichotic performance, as compared with monaural performance, occurred only in the divided-attention condition. These findings are discussed in terms of their implications regarding models of multichannel signal processing and the definition of input channels in terms of earphones.     

Separate "what" and "where" decision mechanisms in processing a dichotic tonal sequence.

Right-handed subjects were presented with a dichotic tonal sequence, whose basic pattern consisted of three 800-Hz tones followed by two 400-Hz tones on the channel and simultaneously three 400-Hz tones followed by two 800-Hz tones on the other. All tones were 250 msec in duration and separated by 250-msec pauses. On any given stimulus presentation, most subjects reported the sequence of pitches delivered to one ear and ignored the other. They further tended significantly to report the sequence delivered to the right ear rather than to the left. However, each tone appeared to be localized in the ear receiving the higher frequency, regardless of which ear was followed for pitch and regardless of whether the higher or lower frequency was in fact perceived.     

Proactive interference of a sequence of tones in a two-tone pitch comparison task

Subjects compared pitches of a standard tone and a comparison tone separated by 1,300–3,000 msec and responded according to whether the comparison tone sounded higher or lower in pitch than the standard tone. Three interfering tones at 300-msec intervals were presented before each pair of tones. Their pitch range varied, being either below or above the pitch of the standard tone; in some of the trials, their pitches were identical to the pitch of the standard tone (no interference). The highest error rate in performance was found when the interfering tones and the comparison tone deviated in the same direction in pitch from the standard tone. In turn, their deviations in the opposite directions resulted in the lowest error rate. This effect was not found to be dependent on whether the interfering tones were randomly ordered or monotonically ordered, together with the standard tone, into melodically ascending/descending sequences. An intermediate error rate in performance was found when the interfering tones and the standard tone were identical. The results support earlier hypotheses, presented in the context of retroactive interference, by demonstrating proactive interference of a tone sequence at the level of representations of individual tones.     

Frequency-shift detectors bind binaural as well as monaural frequency representations

Previous psychophysical work provided evidence for the existence of automatic frequency-shift detectors (FSDs) that establish perceptual links between successive sounds. In this study, we investigated the characteristics of the FSDs with respect to the binaural system. Listeners were presented with sound sequences consisting of a chord of pure tones followed by a single test tone. Two tasks were performed. In the "present/absent" task, the test tone was either identical to one of the chord components or positioned halfway in frequency between two components, and listeners had to discriminate between these two possibilities. In the "up/down" task, the test tone was slightly different in frequency from one of the chord components and listeners had to identify the direction (up or down) of the corresponding shift. When the test tone was a pure tone presented monaurally, either to the same ear as the chord or to the opposite ear, listeners performed the up/down task better than the present/absent task. This paradoxical advantage for directional frequency shifts, providing evidence for FSDs, persisted when the test tone was replaced by a dichotic stimulus consisting of noise but evoking a pitch sensation as a consequence of binaural processing. Performance in the up/down task was similar for the dichotic stimulus and for a monaural narrow-band noise matched in pitch salience to it. Our results indicate that the FSDs are insensitive to sound localization mechanisms and operate on central frequency representations, at or above the level of convergence of the monaural auditory pathways.     

Stimulus intensity, attentional instructions, and the ear advantage during dichotic listening

The present experiment was designed to investigate the effects of the following two variables on the identification of dichotically presented CV syllables: (1) the relative difference in intensity levels of the stimuli presented to the two ears and (2) the instructions to attend to both ears or to focus attention on one ear. As expected for a verbal task, more CV's were identified from the right ear than from the left ear. Furthermore, identification of stimuli presented to one ear improved when (1) those stimuli were relatively higher in volume than the stimuli presented to the other ear and (2) when subjects were instructed to focus attention on only that ear rather than distribute attention across both ears. Of particular importance is the finding that the effects of relative stimulus intensity are the same under conditions of focused attention as under conditions of divided attention. This finding is inconsistent with an attention explantation of the relative intensity effects. Instead, the results are consistent with a model of dichotic listening in which ear of stimulus presentation and relative stimulus intensity influence a perceptual stage of information processing and attentional instructions influence a subsequent response selection stage.     

Binaural loudness gain measured by simple reaction time

In order to yield equal loudness, different studies using scaling or matching methods have found binaural level differences between monaural and diotic presentations ranging from less than 2 dB to as much as 10 dB. In the present study, a reaction time methodology was employed to measure the binaural level difference producing equal reaction time (BLDERT). Participants had to respond to the onset of 1-kHz pure tones with sound pressure levels ranging from 45 to 85 dB, and being presented to the right, the left, or both ears. Equal RTs for monaural and diotic presentation (BLDERTs) were obtained with a level difference of approximately 5 dB. A second experiment showed that different results obtained for the left and right ear are largely due to the responding hand, with ipsilateral responses being faster than contralateral ones. A third experiment investigated the BLDERT for dichotic stimuli, tracing the transition between binaural and monaural stimulation. The results of all three RT experiments are consistent with current models of binaural loudness and contradict earlier claims of perfect binaural summation.     

Synonym and antonym pairs in the detection of dichotically and monaurally presented targets: Competing monaural stimulation can generate a substantial right ear advantage

Aligned pairs of spoken words were presented, and the subject timed in detecting the presence or absence of a prespecified target. The target, if present, was paired with either its synonym or its antonym or an unrelated word. If the target was absent, mutually synonymous, antonymous or unrelated word pairs occured. In experiment 1, presentation of the word pairs was dichotic, and in experiment 2 the same stimuli were now systematically presented to a single ear (competing monaural stimulation). In both cases a strategy of divided attention was imposed with respect to the words. A powerful REA was obtained in the second experiment, demonstrating that this phenomenon does not depend upon occlusion of the ipsilateral by the contralateral auditory pathways (Kimura 1961), but that competition within ears is sufficient. Secondly, the nature of the effect (facilitatory or interfering) from a co-present synonym or antonym of the target depends markedly upon how the ears are stimulated, in partial contrast to and extending the results of Lewis (1970).     

Effect of locus of warning tone on auditory choice reaction time

Forty Ss pressed a left- or right-hand key depending on the ear in which they heard a 500-Hz stimulus tone. Half of the Ss were instructed to press the key on the same side as the ear stimulated (corresponding condition), while the other half pressed the key on the opposite side (noncorresponding condition). A 200-Hz warning tone preceded the stimulus tone by either 200 or 400 msec. The warning tone was presented to the left ear, the right ear, or to both ears in a predetermined random sequence. The locus of the warning tone affected RT on noncorresponding trials but not on corresponding trials. The effect consisted of a significant slowing of information processing on trials where the warning tone was contralateral to the response. Results were explained in terms of an initial tendency to respond toward the source of the warning tone.     

Effects of a contralateral interference tone on auditory recognition

The effects of a contralateral interference tone on identification of the frequency of a brief signal were investigated. The signal was a 20-reset sinusoid and was the same intensity as the 500-msec interference tone. Changes in frequency discrimination were measured as a function of the temporal intee, al between rdgnal and interference tone. Frequency discrimination was unaffected by the presence of a leading interference torte. However, the addition of a trailing interference tone produced a small (about 15%) decrement in performance relative to discriminability measured in quiet. In contrast to the data and supporting theory of Massaro (1970) percent correct identification did not vary appreciably with intertone interval. The present data suggest that interference effects previously obtained with untrained Os ;are greatly attenuated for well-practiced Ss