Neil M. McLachlan

Consonance and pitch.

To date, no consensus exists in the literature as to theories of consonance and dissonance. Experimental data collected over the last century have raised questions about the dominant theories that are based on frequency relationships between the harmonics of music chords. This study provides experimental evidence that strongly challenges these theories and suggests a new theory of dissonance based on relationships between pitch perception and recognition. Experiment 1 shows that dissonance does not increase with increasing numbers of harmonics in chords as predicted by Helmholtzs (1863/1954) roughness theory, nor does it increase with fewer pitch-matching errors as predicted by Stumpfs (1898) tonal fusion theory. Dissonance was strongly correlated with pitch-matching error for chords, which in turn was reduced by chord familiarity and greater music training. This led to the proposition that long-term memory templates for common chords assist the perception of pitches in chords by providing an estimate of the chord intervals from spectral information. When recognition mechanisms based on these templates fail, the spectral pitch estimate is inconsistent with the period of the waveform, leading to cognitive incongruence and the negative affect of dissonance. The cognitive incongruence theory of dissonance was rigorously tested in Experiment 2, in which nonmusicians were trained to match the pitches of a random selection of 2-pitch chords. After 10 training sessions, they rated the chords they had learned to pitch match as less dissonant than the unlearned chords, irrespective of their tuning, providing strong support for a cognitive mechanism of dissonance.

The design of bells with harmonic overtones

Musical bells have had limited application due to the presence of inharmonic partials in the lower part of their acoustic spectra. A series of bells has been designed that contains up to seven partial frequencies in the harmonic series beginning at the fundamental frequency. This was achieved by choosing geometries for finite-element analysis models in which as many purely circumferential bending modes as possible occurred at frequencies below any mode with an axial ring node. The bell models were then fine tuned using gradient projection method shape optimization and the resulting profiles were cast in silicon bronze. A range of bell geometries and timbres is analyzed using psycho-acoustic models and is discussed in relation to European carillon bells.

The Psychological and Physiological Effects of Light and Colour on Space Users

The impact of colour and light conditions on our emotional and physical health and wellbeing is gaining greater importance in our urban societies. While large resources are allocated for well designed buildings with the right choice of colour and lighting conditions, there are little scientific evidence that supports these choices. The aim of this research was to determine the impact of different colours and lighting conditions on people, using non-invasive means. Close correlations between cardiac activity, our emotions and health are well reported in literature and hence it is expected to be a good measure of environmental conditions on people. Electrocardiogram (ECG) is the non-invasive recording of the cardiac activity. Thus, this paper reports experimental research conducted where changes in ECG were measured when the participants were exposed to different colour and light conditions. The results of these experiments show that there is a change in heart rate (HR) due to change in colour and lighting conditions

A computational model of human pitch strength and height judgments.

A synchronization model of pitch processing was extended to include lateral inhibition mechanisms that have been observed in the mammalian mid brain, and information integration mechanisms consistent with observed changes to response fields of mammalian auditory cortex neurons. Model parameters for the inhibition mechanisms were adapted to fit model outputs to observed temporal dynamics of pitch height difference limens from the literature. Pitch strength was defined as the certainty of pitch height judgment, and was calculated by normalizing model responses by their mean. The model was adapted to fit experimental pitch strength data reported in the literature for pure tones and harmonic complexes. It was proposed that pitch height is first estimated in relation to patterns (or templates) of tonotopic activation on the auditory nerve for particular stimulus types. These patterns are stored in long term memory. This pitch height estimation primes cortical pitch neurons to integrate finely tuned pitch information from the inferior colliculus across the periodotopic and tonotopic dimensions. Predicted pitch strength for complexes of unresolved harmonics, iterated rippled noise and amplitude modulated tones using this model also conformed to behavioral data from the literature.

Auditory processing and hallucinations in schizophrenia

The aim of this study was to investigate whether deficits in auditory processing are associated with auditory hallucinations in patients with schizophrenia. It was hypothesised that individuals with a diagnosis of schizophrenia would demonstrate deficits in processing the spectral and temporal aspects of sound and that such deficits would be more pronounced in patients with a history of auditory hallucinations (hallucinators) than those without such a history (non-hallucinators). A community sample meeting clinical criteria for schizophrenia or schizoaffective disorder (19 hallucinators, 15 non-hallucinators) and a matched healthy control group (n=17) completed a broad range of auditory processing tasks involving pitch discrimination of modulated (temporal) and unmodulated (spectral) pure tones, auditory streaming and affective prosodic identification, as well as measures assessing current psychiatric symptoms. In all experimental tasks patients were impaired compared to controls. Specifically hallucinators performed worse than non-hallucinators and controls for pitch discrimination of unmodulated tones and auditory streaming, and both hallucinators and non-hallucinators performed significantly worse than controls for discrimination of modulated tones and affective prosody. These findings suggest that impaired temporal processing may contribute to general difficulties identifying affective speech prosody in patients with schizophrenia, while spectral processing deficits may specifically compromise melodic streaming in hallucinators, which combined with deficits in temporal processing, contribute to the experience of auditory hallucinations.

Cognitive Mechanisms in Chronic Tinnitus: Psychological Markers of a Failure to Switch Attention

The cognitive mechanisms underpinning chronic tinnitus (CT; phantom auditory perceptions) are underexplored but may reflect a failure to switch attention away from a tinnitus sound. Here, we investigated a range of components that influence the ability to switch attention, including cognitive control, inhibition, working memory and mood, on the presence and severity of CT. Our participants with tinnitus showed significant impairments in cognitive control and inhibition as well as lower levels of emotional well-being, compared to healthy-hearing participants. Moreover, the subjective cognitive complaints of tinnitus participants correlated with their emotional well-being whereas complaints in healthy participants correlated with objective cognitive functioning. Combined, cognitive control and depressive symptoms correctly classified 67% of participants. These results demonstrate the core role of cognition in CT. They also provide the foundations for a neurocognitive account of the maintenance of tinnitus, involving impaired interactions between the neurocognitive networks underpinning attention-switching and mood.

A neurocognitive model of recognition and pitch segregation

This paper describes a neurocognitive model of pitch segregation in which it is proposed that recognition mechanisms initiate early in auditory processing pathways so that long-term memory templates may be employed to segregate and integrate auditory features. In this model neural representations of pitch height are primed by the location and pattern of excitation across auditory filter channels in relation to long-term memory templates for common stimuli. Since waveform driven pitch mechanisms may produce information at multiple frequencies for tonal stimuli, pitch priming was assumed to include competitive inhibition that would allow only one pitch estimation at any time. Consequently concurrent pitch information must be relayed to short-term memory via a parallel mechanism that employs pitch information contained in the long-term memory template of the chord. Pure tones, harmonic complexes and two pitch chords of harmonic complexes were correctly classified by the correlation of templates comprising auditory nerve excitation and off-frequency inhibition with the excitation patterns of stimuli. The model then replicated behavioral data for pitch matching of concurrent vowels. Comparison of model outputs to the behavioral data suggests that inability to recognize a stimulus was associated with poor pitch segregation due to the use of inappropriate pitch priming strategies.

Psychological mediators of chronic tinnitus: The critical role of depression

BACKGROUND Maintenance of chronic tinnitus has been proposed to result from a vicious cycle of hypervigilance occurring when a phantom sound is associated with anxiety and limbic system overactivity. Depression, obsessive-compulsiveness, illness attitudes and coping strategies are known to impact tinnitus, but their relationship with the vicious cycle is unknown. As such, we aimed to identify psychological mediators of the vicious cycle. We also examined the relationship between coping strategies and any identified mediators to facilitate the translation of our research to treatment settings. METHODS We comprehensively assessed a heterogeneous community sample of 81 people with chronic tinnitus who completed measures assessing their tinnitus and psychological wellbeing. Specifically, we examined the mediating role of depressive symptoms, illness attitudes, and obsessive-compulsiveness in the vicious cycle. RESULTS While the predicted relationship between tinnitus handicap and anxiety was observed, this was fully mediated by depressive symptoms. In addition, we identified avoidant behaviours and self-blame as maladaptive coping strategies in people with chronic tinnitus and depressive symptoms, identifying potential new treatment targets. LIMITATIONS This work requires replication in a clinical cohort of people with chronic tinnitus, and further investigations of the role of coping strategies. CONCLUSIONS These results extend our understanding of the complex role of psychology in the experience of tinnitus, highlighting the importance of depressive symptoms that may be underpinned by functional disruption of specific neurocognitive networks. We have also identified depressive symptoms and maladaptive coping strategies as new treatment targets to improve the health wellbeing of people with chronic tinnitus.

VISUAL HAND GESTURES CLASSIFICATION USING WAVELET TRANSFORMS

This paper presents a novel technique for classifying human hand gestures based on stationary wavelet transform (SWT) and compares the results with classification based on Hu moments. The technique uses view-based approach for representation of hand actions, and artificial neural networks (ANN) for classification. This approach uses a cumulative image-difference technique where the time between the sequences of images is implicitly captured in the representation of action. This results in the construction of Motion History Images (MHI). These MHIs are decomposed into four sub-images using SWT. The average image (fll) is fed as the global image descriptors to the ANN for classification. The recognition criterion is established using backpropagation based multilayer perceptron (MLP). The preliminary experiments show that such a system can classify human hand gestures with a classification accuracy of 97%. The work is motivated by the previous research in appearance-based motion recognition of human hand actions. The overall goal of our research is to determine the reliability of using this wavelet based computationally inexpensive gesture classification technique that may be used for helping disabled or aged people interact with computers.

WAVELET CLASSIFICATION OF INDOOR ENVIRONMENTAL SOUND SOURCES

Computational auditory scene analysis (CASA) has been attracting growing interest since the publication of Bregmans text on human auditory scene analysis, and is expected to find many applications in data retrieval, autonomous robots, security and environmental analysis. This paper reports on the use of Fourier transforms and wavelet transforms to produce spectral data of sounds from different sources for classification by neural networks. It was found that the multiresolution time-frequency analyses of wavelet transforms dramatically improved classification accuracy when statistical descriptors that captured measures of band limited spectral energy and temporal energy fluctuation were used.