Hemispheric asymmetries for gap detection depend on noise type

Studies of temporal processing asymmetries in the auditory modality have not produced consistent results. Some investigators have found a left hemisphere advantage, but others have failed to replicate this result. The present experiment investigated the possibility that differing properties of the noise employed between these experiments could be responsible for the conflicting results. Short bursts (300 ms) of white or brown noise were delivered monaurally to 42 participants. Half of the stimuli contained 3-5 ms gaps of silence. A right ear (left hemisphere) advantage in accuracy was observed in the white noise condition, but there was no such difference in the brown noise condition. This result demonstrates that the different acoustic properties of the stimuli between experiments can account for some of the discrepancies in their findings, and supports the position that the left hemisphere is superior at processing rapid temporal changes.     

Hemispheric asymmetries for temporal information processing: transient detection versus sustained monitoring

This study investigated functional differences in the processing of visual temporal information between the left and right hemispheres (LH and RH). Participants indicated whether or not a checkerboard pattern contained a temporal gap lasting between 10 and 40 ms. When the stimulus contained a temporal signal (i.e. a gap), responses were more accurate for the right visual field-left hemisphere (RVF-LH) than for the left visual field-right hemisphere (LVF-RH). This RVF-LH advantage was larger for the shorter gap durations (Experiments 1 and 2), suggesting that the LH has finer temporal resolution than the RH, and is efficient for transient detection. In contrast, for noise trials (i.e. trial without temporal signals), there was a LVF-RH advantage. This LVF-RH advantage was observed when the entire stimulus duration was long (240 ms, Experiment 1), but was eliminated when the duration was short (120 ms, Experiment 2). In Experiment 3, where the gap was placed toward the end of the stimulus presentation, a LVF-RH advantage was found for noise trials whereas the RVF-LH advantage was eliminated for signal trials. It is likely that participants needed to monitor the stimulus for a longer period of time when the gap was absent (i.e. noise trials) or was placed toward the end of the presentation. The RH may therefore be more efficient in the sustained monitoring of visual temporal information whereas the LH is more efficient for transient detection.     

Control of responding by location of auditory stimuli: rapid acquisition in monkey and rat

Monkeys require a considerably larger number of trials to bring responding under the control of the location of an auditory stimulus than cats, rats, and bats with the same experimental procedures. The present experiment sought to determine the conditions necessary for rapid acquisition of control of responding by location of noise and tone bursts in the monkey. Monkeys were run in an enclosure that contained four loudspeakers and four manipulanda. Two conditions were used in training. In the adjacent condition, a stimulus (noise or tone burst) was presented through one or other of two speakers and a response on the manipulandum adjacent to the speaker was reinforced with food. In the nonadjacent condition, a stimulus was presented through one of two speakers and a response on a manipulandum remote from the speaker was reinforced with food. Acquisition of control was measured by change in the percentage of reinforced responses during training. In the adjacent condition, responding came under control of location within zero to three sessions. In nonadjacent conditions, the animals required 14 to 20 sessions to come under control of location. These latter numbers are comparable to those reported in the literature for localization discrimination in monkeys.     

Ear advantages for temporal resolution in baboons

On the assumption that temporal resolution underlies an individual's ear advantage for speech perception, one would predict an ear advantage for a temporal resolution task to correlate precisely with an ear advantage for the discrimination of consonant-vowel syllables that differ in their temporal features. A gap detection task that required the resolution of brief silent intervals in bursts of noise was employed to test this hypothesis in four baboons. The findings offer support for such a hypothesis and thus increase the feasibility of an animal model of functional asymmetry in the auditory system.     

Helplessness,stress level,and the coronary-prone behavior pattern

Two experiments were conducted to examine the relationship between stress level and learned helplessness in human subjects. Experiment I subjected subjects to loud or moderate noise in order to induce differential stress. Half of the subjects within each stress group were unable to escape from a series of noise bursts, whereas the other half could terminate each burst by manipulating appropriate switches. After the pretreatment series, the same noise was again delivered to subjects, all of whom could now escape or avoid noise by making an appropriate response on a shuttle box. Inescapable (helplessness) pretreatment interfered with escape learning in the second (test) phase of the study under both levels of stress. Experiment II was a partial replication of the first study using only loud noise. The interference effect during test trials was greater than in the first study. In addition to these findings, measures of a coronary-prone behavior pattern were related to differential susceptibility to the interference effect under both high stress and moderate stress conditions. These results were interpreted in terms of differing perceptions of threat imposed by lack of environmental control.     

Control of responding by location of auditory stimuli: adjacency of sound and response.

Four rhesus monkeys were trained to respond on one key when a one-second noise burst was presented through one speaker and to respond on a second key when the noise burst was presented through a second speaker. The acquisition of stimulus control was studied under three conditions, in each of which the relationship between the sound source and the response-key positions varied: an adjacent condition in which the noise burst was presented through the key and a response on this key was reinforced; a reversed-adjacent condition in which the noise burst was presented through one key and responding on the other key was reinforced: and a nonadiacent condition in which responding on the key nearer the sound was reinforced. Under adjacent conditions, stimulus control developed within one or two sessions. Under reversed and nonadjacent conditions, 10 sessions were required for the development of control. The asymptote of correct responding was the same under each condition in all animals.     

Some properties of auditory memory for rapid formant transitions

In the three experiments reported here, subjects indicate whether two sequentially presented syllables, differing in the place of articulation of an initial stop consonant, are phonernically the same or not. The first experiment finds faster |ldsame” responses to acoustically identical pairs than to pairs that are phonemically identical but acoustically distinct. provided that the second syllable is presented within 400 msec of the first. This is interpreted as indicating the persistence of a memory which preserves auditory information about within-category distinctions. The third experiment shows that this advantage remains when a tone is interposed between the two syllables, but is removed when a brief vowel is similarly interposed. The second experiment presents the second syllable of each pair dichotically with a noise burst, and shows that the size of the right-ear advantage for this reaction time task is reduced when the result of comparisons based on this auditory memory is compatible with the required phonemic decision, but that the right-ear advantage is increased when auditory comparisons would contradict the phonemic relationship.     

Shrinkage in the perceived duration of speech and tone by acoustic replacement1

Abstract: To investigate mechanisms for perceiving the duration of an auditory event, an effect of perceptual grouping upon perceived duration was studied psychophysically. In the first experiment, the perceived duration of a spoken word was measured under three conditions of acoustic continuity (i.e., (a) intact, (b) noise‐replaced, and (c) gap‐replaced) as a function of the duration of the target stimulus. Under the noise‐replaced condition, a portion of the target stimulus was physically replaced with a noise burst. Under the gap‐replaced condition, the replacement was made with a gap. The gap‐replacement resulted in a prominent shrinkage of the perceived duration. In the case of noise‐replacement, the amount of shrinkage was moderate but highly significant, although the word employed was perceived to be phonetically intact. Independent of this effect of replacement, the amount of shrinkage was also affected by the physical duration of the target stimulus. The second experiment tested an effect of noise replacement on the perceived duration of a tone burst. In this case, the noise replacement also shrunk the perceived duration of the non‐speech stimulus. This noise‐induced shrinkage could be regarded as being general for the auditory duration. The phenomenon is discussed in relation to a revised model for perceived duration.     

A comparison of the contrast effects in sound localization in the horizontal and vertical planes

The effect of a background sound on the auditory localization of a single sound source was examined. Nine loudspeakers were arranged crosswise in the horizontal and the median vertical plane. They ranged from -20 degrees to +20 degrees, with the center loudspeaker at 0 degree azimuth and elevation. Using vertical and horizontal centimeter scales, listeners verbally estimated the position of a 500-ms broadband noise stimulus being presented at the same time as a 2 s background sound, emitted by one of the four outer loudspeakers. When the background sound consisted of continuous broadband noise, listeners consistently shifted the apparent target positions away from the background sound locations. This auditory contrast effect, which is consistent with earlier findings, equally occurred in both planes. But when the background sound was changed to a pulse train of noise bursts, the contrast effect decreased in the horizontal plane and increased in the vertical plane. This discrepancy might be due to general differences in the processing of interaural and spectral localization information.     

Functional characteristics of auditory temporal-spatial short-term memory: evidence from serial order errors

The functional characteristics of auditory temporal-spatial short-term memory were explored in 8 experiments in which the to-be-remembered stimuli were sequences of bursts of white noise presented in spatial locations separated in azimuth. Primacy and recency effects were observed in all experiments. A 10-s delay impaired recall for primacy and middle list items but not recency. This effect was shown not to depend on the response modality or on the incidence of omissions or repetitions. Verbal and nonverbal secondary tasks did not affect memory for auditory spatial sounds. Temporal errors rather than spatial errors predominated, suggesting that participants were engaged in a process of maintaining order. This pattern of results may reflect characteristics that serial recall has in common with verbal and spatial recall, but some are unique to the representation of memory for temporal-spatial auditory events.     

Monaural and binaural audiogenic seizures in mice

The progression of sound-induced seizures was examined in unilaterally or bilaterally sensitized SJL/J mice tested either monaurally or binaurally. An unexpected right-side advantage for becoming susceptible to audiogenic seizure was observed. In addition, two distinct patterns of seizure progression were noted, a uniphasic sequence in which a single burst of running preceded the convulsion and a biphasic pattern with two such bursts. The biphasic progression is viewed to be the result of unilaterally initiated seizures and characteristically reached only a clonic level of severity. Uniphasic seizures are concluded to be the result of bilaterally initiated seizures and, when they occurred after more than 30 s of auditory stimulation, frequently reached a tonic level of intensity. The present results support the view that audiogenic seizures are characterized by precisely timed, sequential processes dependent upon the specific priming and test procedures employed.     

Effects of unit formation on the perception of a changing sound

The effects of subunit formation on adult listeners' ability to notice changes in a continuous spectral gradient of sound were studied. Results of this experiment support the idea that the auditory system processes information differently within a unit, and that this processing does not occur unless the perceptual system detects unit boundaries. In this experiment, silences were inserted into a continuously changing sound to cause the formation of short units. Listeners noticed the change earlier in conditions with silences inserted than in to conditions where the transition was either unbroken or broken by loud noise bursts. Results are discussed in terms of two processes, one that accentuates stimulus properties present at moments of onset and offset, and a second that uses onsets and offsets to signal the beginnings and ends of units and reduces the change perceived within units.     

Effects of unit formation on the perception of a changing sound

The effects of subunit formation on adult listeners' ability to notice changes in a continuous spectral gradient of sound were studied. Results of this experiment support the idea that the auditory system processes information differently within a unit, and that this processing does not occur unless the perceptual system detects unit boundaries. In this experiment, silences were inserted into a continuously changing sound to cause the formation of short units. Listeners noticed the change earlier in conditions with silences inserted than in to conditions where the transition was either unbroken or broken by loud noise bursts. Results are discussed in terms of two processes, one that accentuates stimulus properties present at moments of onset and offset, and a second that uses onsets and offsets to signal the beginnings and ends of units and reduces the change perceived within units.     

The monaural localization of tonal stimuli

With one ear occluded, 17 listeners were asked to locate tone bursts, .25, 4, .6, .9. l.4, 2.0, 3.2, 4.8, and 7.2 kHz, generated by a loudspeaker concealed from view. The S’s response was to callout that number, from a series of numbers arranged horizontally, behind which he thought the tone bursts originated. The listeners perceived the sounds as emanating from the side of the unoccluded ear, but their judgments bore no consistent relation to the actual location of the sound source. Rather, the listeners showed a strong tendency to locate a tone burst, within the range of .9 through 7.2 kHz, in a fixed spatial relation to the next higher- and lower-pitched tone burst. Distorting the pinna of the unoccluded ear failed to modify the perceptual pattern. It was suggested that the perceived spatial relations among the various frequencies was a by-product of the tonotopic organization of the auditory nervous system.     

Rapid adaptation to auditory-visual spatial disparity

The so-called ventriloquism aftereffect is a remarkable example of rapid adaptative changes in spatial localization caused by visual stimuli. After exposure to a consistent spatial disparity of auditory and visual stimuli, localization of sound sources is systematically shifted to correct for the deviation of the sound from visual positions during the previous adaptation period. In the present study, this aftereffect was induced by presenting, within 17 min, 1800 repetitive noise or pure-tone bursts in combination with synchronized, and 20° disparate flashing light spots, in total darkness. Post-adaptive sound localization, measured by a method of manual pointing, was significantly shifted 2.4° (noise), 3.1° (1 kHz tones), or 5.8° (4 kHz tones) compared with the pre-adaptation condition. There was no transfer across frequencies; that is, shifts in localization were insignificant when the frequencies used for adaptation and the post-adaptation localization test were different. It is hypothesized that these aftereffects may rely on shifts in neural representations of auditory space with respect to those of visual space, induced by intersensory spatial disparity, and may thus reflect a phenomenon of neural short-term plasticity.     

Representational momentum in spatial hearing

The final position of a moving visual object usually appears to be displaced in the direction of motion. We investigated this phenomenon, termed representational momentum, in the auditory modality. In a dark anechoic environment, an acoustic target (continuous noise or noise pulses) moved from left to right or from right to left along the frontal horizontal plane. Listeners judged the final position of the target using a hand pointer. Target velocity was 8 degrees s(-1) or 16 degrees s(-1). Generally, the final target positions were localised as displaced in the direction of motion. With presentation of continuous noise, target velocity had a strong influence on mean displacement: displacements were stronger with lower velocity. No influence of sound velocity on displacement was found with motion of pulsed noise. Although these findings suggest that the underlying mechanisms may be different in the auditory and visual modality, the occurrence of displacements indicates that representational-momentum-like effects are not restricted to the visual modality, but may reflect a general phenomenon with judgments of dynamic events.     

Echo suppression and discrimination suppression aspects of the precedence effect

The precedence effect is a phenomenon that may occur when a sound from one direction (the lead) is followed within a few milliseconds by the same or a similar sound from another direction (the lag, or the echo). Typically, the lag sound is not heard as a separate event, and changes in the lag sound’s direction cannot be discriminated. The hypothesis is proposed in this study that these two aspects of precedence (echo suppression and discrimination suppression) are at least partially independent phenomena. Two experiments were conducted in which pairs of noise bursts were presented to subjects from two loudspeakers in the horizontal plane to simulate a lead sound and a lag sound (the echo). Echo suppression threshold was measured as the minimum echo delay at which subjects reported hearing two sounds rather than one sound; discrimination suppression threshold was measured as the minimum echo delay at which subjects could reliably discriminate between two positions of the echo. In Experiment 1, it was found that echo suppression threshold was the same as discrimination suppression threshold when measured with a single burst pair (average 5.4 msec). However, when measured after presentation of a train of burst pairs (a condition that may produce “buildup of suppression”), discrimination suppression threshold increased to 10.4 msec, while echo suppression threshold increased to 26.4 msec. The greater buildup of echo suppression than of discrimination suppression indicates that the two phenomena are distinct under buildup conditions and may be the reflection of different underlying mechanisms. Experiment 2 investigated the effect of the directional properties of the lead and lag sounds on discrimination suppression and echo suppression. There was no consistent effect of the spatial separation between lead and lag sources on discrimination suppression or echo suppression, nor was there any consistent difference between the two types of thresholds (overall average threshold was 5.9 msec). The negative result in Experiment 2 may have been due to the measurements being obtained only for single-stimulus conditions and not for buildup conditions that may involve more central processing by the auditory system.     

Quantifying temporal ventriloquism in audiovisual synchrony perception

The integration of visual and auditory inputs in the human brain works properly only if the components are perceived in close temporal proximity. In the present study, we quantified cross-modal interactions in the human brain for audiovisual stimuli with temporal asynchronies, using a paradigm from rhythm perception. In this method, participants had to align the temporal position of a target in a rhythmic sequence of four markers. In the first experiment, target and markers consisted of a visual flash or an auditory noise burst, and all four combinations of target and marker modalities were tested. In the same-modality conditions, no temporal biases and a high precision of the adjusted temporal position of the target were observed. In the different-modality conditions, we found a systematic temporal bias of 25–30 ms. In the second part of the first and in a second experiment, we tested conditions in which audiovisual markers with different stimulus onset asynchronies (SOAs) between the two components and a visual target were used to quantify temporal ventriloquism. The adjusted target positions varied by up to about 50 ms and depended in a systematic way on the SOA and its proximity to the point of subjective synchrony. These data allowed testing different quantitative models. The most satisfying model, based on work by Maij, Brenner, and Smeets (Journal of Neurophysiology 102, 490–495, 2009), linked temporal ventriloquism and the percept of synchrony and was capable of adequately describing the results from the present study, as well as those of some earlier experiments.     

Validity and boundary conditions of automatic response activation in the Simon task.

Three experiments were conducted to determine whether spatial stimulus-response compatibility effects are caused by automatic response activation by stimulus properties or by interference between codes during translation of stimulus into response coordinates. The main evidence against activation has been that in a Simon task with hands crossed, responses are faster at the response location ipsilateral to the stimulus though manipulated by the hand contralateral to the stimulus. The experiments were conducted with hands in standard and in crossed positions and electroencephalogram measures showed coactivation of the motor cortex induced by stimulus position primarily during standard hand positions with visual stimuli. Only in this condition did the Simon effect decay with longer response times. The visual Simon effect appeared to be due to specific mechanisms of visuomotor information transmission that are not responsible for the effects obtained with crossed hands or auditory stimuli.     

Effects of tobacco smoking, schizotypy and number of pre-exposures on latent inhibition in healthy subjects

Latent inhibition is a slowing of learning about a stimulus that when previously experienced had no consequences. This study investigated the effects of tobacco smoking and personality traits on a latent inhibition task. Two-hundred and five healthy adults performed an auditory masking task during which half of them were pre-exposed to bursts of white noise. All subjects were then asked to detect an association of the white noise with a change on a computer screen. Subjects who had heard the white noises before were slower to learn the association than subjects who had not, i.e. they showed latent inhibition. Latent inhibition was stronger when subjects were pre-exposed to 10 rather than 6 bursts of white noise. Latent inhibition was reduced in subjects who smoked tobacco and in non-smoking subjects who scored highly on a schizotypy questionnaire. These two effects were independent. We conclude that tobacco smoking should be taken into account in interpreting the results of human latent inhibition studies.