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Timothy D Griffiths

Publications and source records attributed to Timothy D Griffiths.

At least 19 recordsLinked to original sources
PubMed2006

Morphometry of the amusic brain: a two-site study.

Congenital amusia (or tone deafness) is a lifelong disability that prevents otherwise normal-functioning individuals from developing basic musical skills. Behavioural evidence indicates that congenital amusia is due to a severe deficit in pitch processing, but very little is known about the neural correlates of this condition. The objective of the present study was to investigate the structural neural correlates of congenital amusia. To this aim, voxel-based morphometry was used to detect brain anatomical differences in amusic individuals relative to musically intact controls, by analysing T1-weighted magnetic resonance images from two independent samples of subjects. The results were consistent across samples in highlighting a reduction in white matter concentration in the right inferior frontal gyrus of amusic individuals. This anatomical anomaly was correlated with performance on pitch-based musical tasks. The results are consistent with neuroimaging findings implicating right inferior frontal regions in musical pitch encoding and melodic pitch memory. We conceive the present results as a consequence of an impoverished communication in a right-hemisphere-based network involving the inferior frontal cortex and the right auditory cortex. Moreover, the data point to the integrity of white matter tracts in right frontal brain areas as being key in acquiring normal musical competence.

Auditory Perceptual Disorders↗
PubMed2006

Representation of interaural time delay in the human auditory midbrain.

Interaural time difference (ITD) is a critical cue to sound-source localization. Traditional models assume that sounds leading at one ear, and perceived on that side, are processed in the opposite midbrain. Using functional magnetic resonance imaging we demonstrate that as the ITDs of sounds increase, midbrain activity can switch sides, even though perceived location remains on the same side. The data require a new model for human ITD processing.

Acoustic Stimulation↗
PubMed2006

Music and the brain: disorders of musical listening.

The study of the brain bases for normal musical listening has advanced greatly in the last 30 years. The evidence from basic and clinical neuroscience suggests that listening to music involves many cognitive components with distinct brain substrates. Using patient cases reported in the literature, we develop an approach for understanding disordered musical listening that is based on the systematic assessment of the perceptual and cognitive analysis of music and its emotional effect. This approach can be applied both to acquired and congenital deficits of musical listening, and to aberrant listening in patients with musical hallucinations. Both the bases for normal musical listening and the clinical assessment of disorders now have a solid grounding in systems neuroscience.

Auditory Perception↗
PubMed2006

Rhythm deficits in 'tone deafness'.

It is commonly observed that 'tone deaf' individuals are unable to hear the beat of a tune, yet deficits on simple timing tests have not been found. In this study, we investigated rhythm processing in nine individuals with congenital amusia ('tone deafness') and nine controls. Participants were presented with pairs of 5-note sequences, and were required to detect the presence of a lengthened interval. In different conditions the sound sequences were presented isochronously or in an integer-ratio rhythm, and these were either monotonic or varied randomly in pitch. It was found that the 'tone deaf' participants exhibited inferior rhythm analysis for the sequences that varied in pitch compared to those that did not, whereas the controls obtained equivalent thresholds for these two conditions. These results suggest that the rhythm deficits in congenital amusia result from the pitch-variations in music.

Acoustic Stimulation↗
PubMed2004

Musically tone-deaf individuals have difficulty discriminating intonation contours extracted from speech.

Musically tone-deaf individuals have psychophysical deficits in detecting pitch changes, yet their discrimination of intonation contours in speech appears to be normal. One hypothesis for this dissociation is that intonation contours use coarse pitch contrasts which exceed the pitch-change detection thresholds of tone-deaf individuals (). We test this idea by presenting intonation contours for discrimination, both in the context of the original sentences in which they occur and in a "pure" form dissociated from any phonetic context. The pure form consists of gliding-pitch analogs of the original intonation contours which exactly follow their pattern of pitch and timing. If the spared intonation perception of tone-deaf individuals is due to the coarse pitch contrasts of intonation, then such individuals should discriminate the original sentences and the gliding-pitch analogs equally well. In contrast, we find that discrimination of the gliding-pitch analogs is severely degraded. Thus it appears that the dissociation between spoken and musical pitch perception in tone-deaf individuals is due to a deficit at a higher level than simple pitch-change detection.

Adult↗
PubMed2004

Characterization of deficits in pitch perception underlying 'tone deafness'.

Congenital amusia is a disorder characterized by life-long, selective deficits in the perception of music. This study examined pitch-perception abilities in a group of 10 adults with this disorder. Tests were administered that assessed fine-grained pitch perception by determining thresholds both for the detection of continuous and segmented pitch changes, and for the recognition of pitch direction. Tests were also administered that assessed the perception of more complex pitch patterns, using pitch-sequence comparison tasks. In addition, the perceptual organization of pitch was also examined, using stream segregation tasks that assess the assignment of sounds differing in pitch to one or two distinct perceptual sources. In comparison with 10 control subjects, it was found that the participants with congenital amusia exhibited deficits both at the level of detecting fine-grained differences in pitch, and at the level of perceiving patterns in pitch. In contrast, no abnormalities were identified in the perceptual organization of pitch. The pitch deficits identified are able to account for the music perception difficulties in this disorder, and implicate deficient cortical processing.

Acoustic Stimulation↗
PubMed2004

Training improves acoustic pattern perception.

Pitch changes that occur in speech and melodies can be described in terms of contour patterns of rises and falls in pitch and the actual pitches at each point in time. This study investigates whether training can improve the perception of these different features. One group of ten adults trained on a pitch-contour discrimination task, a second group trained on an actual-pitch discrimination task, and a third group trained on a contour comparison task between pitch sequences and their visual analogs. A fourth group did not undergo training. It was found that training on pitch sequence comparison tasks gave rise to improvements in pitch-contour perception. This occurred irrespective of whether the training task required the discrimination of contour patterns or the actual pitch details. In contrast, none of the training tasks were found to improve the perception of the actual pitches in a sequence. The results support psychological models of pitch processing where contour processing is an initial step before actual pitch details are analyzed. Further studies are required to determine whether pitch-contour training is effective in improving speech and melody perception.

Acoustic Stimulation↗
PubMed2004

Cortical processing of complex sound: a way forward?

The organization of the cortical auditory system remains controversial. In particular, the extent to which there is regional specialization in the cortical processing of complex sound is unclear. Here, we ask whether we are currently asking the right questions of auditory cortex, or using the appropriate techniques to do so. A key factor that will promote such understanding in the future will be increasing dialogue between workers using electrophysiological recording methods to assess the response properties of single neurons and those using imaging techniques to map regional organization. In the future, further insights will be obtained by efforts to test hypotheses developed on the basis of one approach by the use of the other. Imaging can tell the neurophysiologists where to look, and work on single neurons can constrain network models based on imaging. There is a crucial need for better understanding of the anatomy of the auditory cortex in different species and for comparative studies that will underpin both approaches.

Acoustic Stimulation↗
PubMed2004

What is an auditory object?

Objects are the building blocks of experience, but what do we mean by an object? Increasingly, neuroscientists refer to 'auditory objects', yet it is not clear what properties these should possess, how they might be represented in the brain, or how they might relate to the more familiar objects of vision. The concept of an auditory object challenges our understanding of object perception. Here, we offer a critical perspective on the concept and its basis in the brain.

Acoustic Stimulation↗
PubMed2003

Absence of auditory 'global interference' in autism.

There has been considerable recent interest in the cognitive style of individuals with Autism Spectrum Disorder (ASD). One theory, that of weak central coherence, concerns an inability to combine stimulus details into a coherent whole. Here we test this theory in the case of sound patterns, using a new definition of the details (local structure) and the coherent whole (global structure). Thirteen individuals with a diagnosis of autism or Asperger's syndrome and 15 control participants were administered auditory tests, where they were required to match local pitch direction changes between two auditory sequences. When the other local features of the sequence pairs were altered (the actual pitches and relative time points of pitch direction change), the control participants obtained lower scores compared with when these details were left unchanged. This can be attributed to interference from the global structure, defined as the combination of the local auditory details. In contrast, the participants with ASD did not obtain lower scores in the presence of such mismatches. This was attributed to the absence of interference from an auditory coherent whole. The results are consistent with the presence of abnormal interactions between local and global auditory perception in ASD.

Acoustic Stimulation↗
PubMed2003

A neural basis for the perception of voices in external auditory space.

We used functional imaging of normal subjects to identify the neural substrate for the perception of voices in external auditory space. This fundamental process can be abnormal in psychosis, when voices that are not true external auditory objects (auditory verbal hallucinations) may appear to originate in external space. The perception of voices as objects in external space depends on filtering by the outer ear. Psychoses that distort this process involve the cerebral cortex. Functional magnetic resonance imaging was carried out on 12 normal subjects using an inside-the-scanner simulation of 'inside head' and 'outside head' voices in the form of typical auditory verbal hallucinations. Comparison between the brain activity associated with the two conditions allowed us to test the hypothesis that the perception of voices in external space ('outside head') is subserved by a temperoparietal network comprising association auditory cortex posterior to Heschl's gyrus [planum temporale (PT)] and inferior parietal lobule. Group analyses of response to 'outside head' versus 'inside head' voices showed significant activation solely in the left PT. This was demonstrated in three experiments in which the predominant lateralization of the stimulus was to the right, to the left or balanced. These findings suggest a critical involvement of the left PT in the perception of voices in external space that is not dependent on precise spatial location. Based on this, we suggest a model for the false perception of externally located auditory verbal hallucinations.

Acoustics↗
PubMed2003

Functional imaging of pitch analysis.

This work addresses the brain basis for the analysis of pitch and pitch patterns required for normal musical perception. Recent functional imaging experiments are consistent with a hierarchical scheme for the analysis of pitch. Mechanisms in the ascending auditory pathway to the primary auditory cortex allow the representation of the spectral and temporal features of individual notes required for the perception of their pitch. Converging experiments where pitch strength is manipulated in different ways suggest that there may be a "pitch center" in the lateral part of Heschl's gyrus, adjacent to the primary auditory area. The suggestion is that there is a representation in this area that correlates with the perception of pitch rather than a simple mapping of physical stimulus characteristics. The analysis of patterns of pitch such as melodies, as opposed to the pitch of individual notes, involves much more distributed processing in the superior temporal lobes and frontal lobes. Involvement of the frontal lobe in pitch pattern analysis may in part reflect whether subjects analyze the pitch patterns in order to carry out an output task.

Auditory Pathways↗
PubMed2003

Analyzing pitch chroma and pitch height in the human brain.

The perceptual pitch dimensions of chroma and height have distinct representations in the human brain: chroma is represented in cortical areas anterior to primary auditory cortex, whereas height is represented posterior to primary auditory cortex.

Auditory Cortex↗
PubMed2003

Laterality effects in perceived spatial location of hallucination-like voices.

Aydin and colleagues reported a reversal of physiological 'right-ear advantage' in a group of right-handed patients with schizophrenia, using an auditory acuity test. In schizophrenia, auditory hallucinations may appear to be spatially located inside or outside the patient's head. Here we show, using virtual acoustic space techniques, that normal right-handed subjects have a right-ear advantage for correctly locating the 'source' of hallucination-like voices as from either inside or outside the head. We propose a model for understanding lateralised, external hallucinations in schizophrenia based upon reversal of normal cortical asymmetry for auditory spatial processing.

Adult↗
PubMed2002

The processing of temporal pitch and melody information in auditory cortex.

An fMRI experiment was performed to identify the main stages of melody processing in the auditory pathway. Spectrally matched sounds that produce no pitch, fixed pitch, or melody were all found to activate Heschl's gyrus (HG) and planum temporale (PT). Within this region, sounds with pitch produced more activation than those without pitch only in the lateral half of HG. When the pitch was varied to produce a melody, there was activation in regions beyond HG and PT, specifically in the superior temporal gyrus (STG) and planum polare (PP). The results support the view that there is hierarchy of pitch processing in which the center of activity moves anterolaterally away from primary auditory cortex as the processing of melodic sounds proceeds.

Acoustic Stimulation↗
PubMed2002

A common cortical substrate activated by horizontal and vertical sound movement in the human brain.

Perception of movement in acoustic space depends on comparison of the sound waveforms reaching the two ears (binaural cues) as well as spectrotemporal analysis of the waveform at each ear (monaural cues). The relative importance of these two cues is different for perception of vertical or horizontal motion, with spectrotemporal analysis likely to be more important for perceiving vertical shifts. In humans, functional imaging studies have shown that sound movement in the horizontal plane activates brain areas distinct from the primary auditory cortex, in parietal and frontal lobes and in the planum temporale. However, no previous work has examined activations for vertical sound movement. It is therefore difficult to generalize previous imaging studies, based on horizontal movement only, to multidimensional auditory space perception. Using externalized virtual-space sounds in a functional magnetic resonance imaging (fMRI) paradigm to investigate this, we compared vertical and horizontal shifts in sound location. A common bilateral network of brain areas was activated in response to both horizontal and vertical sound movement. This included the planum temporale, superior parietal cortex, and premotor cortex. Sounds perceived laterally in virtual space were associated with contralateral activation of the auditory cortex. These results demonstrate that sound movement in vertical and horizontal dimensions engages a common processing network in the human cerebral cortex and show that multidimensional spatial properties of sounds are processed at this level.

Acoustic Stimulation↗