Advancing textural heterogeneity: Effect of manipulating multi-component model foods on the perception of textural complexity.

The aim of this study was to identify the individual and interacting effects of varying the mechanical properties of two inserts (к-carrageenan beads; 1, 2 and 4% w/w and/or agar-based disks; 0.3, 1.2 and 3% w/w) in pectin-based gels on the perception of textural complexity. A full factorial design was utilised, 16 samples were characterised with sensory and instrumental tests. Rate-All-That-Apply (RATA) was performed by 50 untrained participants. RATA selection frequency provided different information to attribute intensity regarding the detection of low yield stress inserts. In the two-component samples, the perception of textural complexity (n = 89) increased with insert yield stress for both к-carrageenan beads and agar disks. However, with the addition of medium and high yield stress к-carrageenan beads to three-component samples, the increases in perceived textural complexity caused by increased agar yield stress were eliminated. The definition of textural complexity, the number and intensity of texture sensations, as well as their interactions and contrasts, was in line with the results, and the hypothesis that not only mechanical properties but also the interaction of components play a key role in the perception of textural complexity.

Can binaural beats facilitate autonomic recovery following exposure to an acute stressor?

BACKGROUND AND PURPOSE: Binaural beats are seen as a new type of 'digital-drug'. The aim of this study was to determine if binaural beats could facilitate physiological recovery from a mental stressor. MATERIALS AND METHODS: 92 adults were exposed five times each to a 2-min mental stressor and a subsequent 4-min rest period containing silence or 1-of-4 examples of binaural beats (2, 5, 10, and 24 Hz). Physiological recovery across the five rest periods, as measured using skin conductance, heart rate, and breathing, were compared using one-way analysis of variance. RESULTS: Binaural beats were linked to enhanced physiological recovery relative to silence. However, the expected pattern of results whereby lower frequency binaural beats would be associated with greater physiological recovery, was not observed. CONCLUSION: Our findings do not support a relationship between binaural beats and systematic changes in emotional states as measured physiologically. On the basis of our results the acute administration of binaural beats in primary care to lower sympathetic arousal cannot yet be considered an evidence-based practice.

Electrophysiological indices of amplitude modulated sounds and sensitivity to noise.

Annoyance to unwanted sound differs across individuals, though why noise sensitive individuals are more reactive to noise while others are more resilient remains unanswered. The Information Processing Hypothesis posits that noise sensitive individuals are vulnerable to higher-order auditory processing deficits. The aim of this study was to test the veracity of this hypothesis by documenting differences in pre-attentive auditory evoked potentials (ERP) between high noise sensitive and low noise sensitive individuals. Participants provided annoyance measures for three amplitude-modulated sounds, and were exposed to the sounds while undergoing electroencephalogram recording. Results indicated that annoyance increased with modulation, and that modulation affected both N1 and P2 components. At the group level, highly noise sensitive individuals exhibited significantly greater annoyance to a low-frequency tone, alongside significantly higher P2 amplitude, than individuals reporting low levels of noise sensitivity. Overall, the results partially supported the Information Processing Hypothesis of noise sensitivity, but also suggest that acoustic features may be more important than hitherto argued.

Electrophysiological approaches to noise sensitivity.

BACKGROUND: Noise sensitivity describes an individual's general reactivity to sound. It is a common trait found in many clinical populations and describes approximately 20% of the general population. Little is known about its underlying mechanisms, however. OBJECTIVES: Here we present findings from three studies designed to expose differences in electrophysiological measures between noise-sensitive and noise-resistant individuals. METHOD: Noise sensitivity was estimated using self-report measures, while electrophysiological indices included both cardiac (heart rate, heart rate variability) and electroencephalographic (event-related potential) measures. All three studies were designed with reference to preexisting theoretical frameworks. RESULTS: Significant differences in heart rate change and heart rate variability indices between noise-sensitive and noise-resistant groups were found. Further, the noise-sensitive group exhibited less sensory gating than the noise-resistant group. CONCLUSIONS: While the findings from all three studies were not definitive in indicating a likely biological mechanism underlying noise sensitivity, they do suggest that electrophysiological investigation of noise sensitivity is viable and has potential to inform clinical research into a relatively understudied symptom.

Masking functions and fixed-signal functions for low-level 1000-Hz tones.

Masking functions and fixed-signal functions were constructed using a narrow range of pedestal intensities for 10-ms, 1000-Hz gated tones. Data from three experiments agreed with previously reported data, clearly demonstrating negative masking and the pedestal effect. The data extend earlier findings by showing (1) the resilience of the pedestal effect when a background noise masker is introduced; (2) a possible indifference of the fixed-signal function to stimulus duration; (3) the ability of a set of psychometric functions to produce both masking and fixed-signal functions; (4) depending on method, the impact of unit choice on the interpretation of both the pedestal effect and negative masking data. Results are discussed in relation to current psychophysical models, and suggest that accounting for the auditory system's sensitivity to differences in low-level sounds remains a challenge.

Processing of binaural spatial information in human auditory cortex: neuromagnetic responses to interaural timing and level differences.

This study was designed to test two hypotheses about binaural hearing: (1) that binaural cues are primarily processed in the hemisphere contralateral to the perceived location of a sound; and (2) that the two main binaural cues, interaural timing differences and interaural level differences, are processed in separate channels in the auditory cortex. Magnetoencephalography was used to measure brain responses to dichotic pitches--a perception of pitch created by segregating a narrow band of noise from a wider band of noise--derived from interaural timing or level disparities. Our results show a strong modulation of interhemispheric M100 amplitudes by ITD cues. When these cues simulated source presentation unilaterally from the right hemispace, M100 amplitude changed from a predominant right hemisphere pattern to a bilateral pattern. In contrast, ILD cues lacked any capacity to alter the right hemispheric distribution. These data indicate that intrinsic hemispheric biases are large in comparison to any contralaterality biases in the auditory system. Importantly, both types of binaural cue elicited a circa 200 ms latency object-related negativity component, believed to reflect automatic cortical processes involved in distinguishing concurrent auditory objects. These results support the conclusion that ITDs and ILDs are processed by distinct neuronal populations to relatively late stages of cortical processing indexed by the M100. However information common to the two cues seems to be extracted for use in a subsequent stage of auditory scene segregation indexed by the object related negativity. This may place a new bound on the extent to which sound location cues are processed in separate channels of the auditory cortex.

Evidence of stochastic resonance in an auditory discrimination task may reflect response bias.

Stochastic resonance is a mechanism that improves the detection of weak periodic signals when an optimal level of background noise is present. This counterintuitive concept is thought to involve a cooperative effect that arises out of a physical coupling between deterministic and random dynamics in nonlinear systems. We report the results of three psychophysical experiments designed to probe the auditory system for evidence of stochastic resonance. In all three experiments, participants judged which of two 1000-Hz tones was greater in intensity, with one of the tones embedded in a background of Gaussian noise. Experiment 1 used a two-alternative forced choice task and provided evidence of enhanced discriminability at an optimal level of noise. The aim of Experiment 2 was to determine whether the apparent enhancement observed in Experiment 1 was due to sensory processes or to a response bias. Receiver operating characteristic analysis supported an explanation based on decision processes, rather than a genuine sensory enhancement. An additional experiment (Experiment 3) was used to discount experimental artifacts.

Event-related potentials for interaural time differences and spectral cues.

Dichotic pitches and mistuned harmonics can each lead to the perception of one or two auditory objects. Comparison of event-related potentials for the perception of one versus two objects reveals an early negative and a late positive component. The relationship of these components with auditory segregation was further investigated using stimuli containing monaural spectral cues to pitch, binaural timing cues to pitch, or a combination of both, interleaved with control stimuli (no pitch). Stimuli containing timing cues or a combination of timing and spectral cues reliably elicited both components, which were of larger amplitude when both cues were present. For stimuli containing only spectral cues, the early component was attenuated in amplitude and no measurable late component was detected.

Sequential processing of interaural timing differences for sound source segregation and spatial localization: evidence from event-related cortical potentials.

Cortical processing of interaural timing differences (ITDs) was investigated with event-related potential (ERP) measurements in 16 human participants who were required in separate tasks to detect or to spatially localize dichotically embedded pitches. ITDs elicited three ERP components labeled ORN, N2, and P400. The ORN occurred at a latency of 150-250 ms and was elicited by ITDs regardless of location or task. In contrast, the N2 response (250-350 ms) was strongly modulated by location and showed larger amplitudes for the localization task than for the detection task. Finally, ITDs in the detection task elicited a P400 at a latency of 400-500 ms, but this response was entirely absent from ERPs elicited by identical stimuli in the localization task. These results are consistent with a sequential model of auditory perception in which segregation of concurrent sounds is followed by domain-specific processing of object location and identity.

Graded cue information in dichotic pitch: effects on event-related potentials.

To determine whether electroencephalogram components elicited by dichotic pitch stimuli are all-or-none threshold-like responses or graded responses that depend on the saliency of the stimuli, we recorded electroencephalograms while participants listened to dichotic pitch stimuli constructed with different signal-to-background ratios. The object-related negativity and P400 components were largest when the dichotic pitch was most salient (high signal-to-background ratio), and decreased in amplitude with decreasing signal-to-background ratio. These results are similar to those reported for mistuned harmonics, thereby providing additional evidence that the object-related negativity and P400 components observed for these disparate stimulus types reflect similar processing. They also support the notion that the object-related negativity and P400 amplitudes are dependent on the level of relevant cue-based stimulus information.

Differential cortical processing of location and pitch changes in dichotic pitch.

The objective of this study was to determine whether the auditory mismatch negativity can be elicited by changes in spatial and nonspatial cues within dichotic pitches. Participants were presented with blocks of standard dichotic pitch stimuli in which location or pitch was occasionally varied. A mismatch negativity was reliably elicited by deviant locations; in contrast, no measurable mismatch negativity response was found for deviant pitches. A separate psychophysical screening procedure ruled out the possibility that participants could not hear the pitch deviations. The results indicate that spatial and nonspatial features of dichotic pitch receive differential processing at a preattentive level of analysis within the auditory system and are supportive of recent notions of dual processing streams in audition.

Detection-theoretic analysis of same-different judgments for the amplitude discrimination of acoustic sinusoids.

Three methods were applied to determine which decision model best accounted for same-different judgments about the amplitude of acoustic sinusoids. The methods were (1) analysis of the shape of the receiver operating characteristic; (2) analysis of an observer's decision space; and (3) a correlation method based on the conditional-on-single-stimulus procedure. In one experiment, observers rated their confidence that a pair of 1-kHz sinusoids was drawn from the same or from different sets. The two sets had identical Gaussian distributions of decibel amplitudes, but their mean amplitudes differed by 3 dB. The differencing model, in which observers base their decision on the absolute difference between the two observations, accounted for the data better than the independent-observation model, in which observers compute independent likelihood ratios for each observation. A second experiment added to every trial an interval that contained a 1-kHz sinusoid whose amplitude equaled the grand mean of both stimulus sets. Despite this additional information, which is needed to adopt the independent-observation model, the differencing model again better accounted for the data.