Hearing in the Mind's Ear: A PET Investigation of Musical Imagery and Perception

Inferior colliculus as candidate for pitch extraction: multiple support from statistics of bilateral spontaneous otoacoustic emissions

The fibrodendritic laminae of the central nucleus of the inferior colliculus (ICC) constitute a frequency map in stacked sheets that are consistently related to the psychoacoustic critical bandwidth (CB) [Schreiner and Langner, 1997. Nature 388, 383-386]. The recently observed co-occurrence of the CB and the double CB (2CB) suggested an adaptation of the ICC frequency map to the extraction of the fundamental frequency f(0) [Braun, 1999. Hear. Res. 129, 71-82]. The present study examined a possible influence of this frequency map upon efferent signaling towards the cochlea. The f(0) distribution of 2890 monaural and 2604 binaural pairs of human spontaneous otoacoustic emissions was analyzed by three statistical methods and in each case showed non-random behavior in the CB-2CB range. Single results were (1) a bias of right ear f(0) (mode at 349 Hz) and left ear f(0) (mode at 262 Hz) towards different ranges of speech f(0) (P<0.02); (2) a bias of binaural, but not monaural, f(0) towards five of 12 semitone bins, C-G-D-A-E, representing the most frequent tones in music (P<0.003); (3) a bias of binaural, but not monaural, f(0) fine-distribution towards the exact pitch frequencies used in music, according to the international standard A4=440 Hz (P=0.03). The results support a model of lamina-based f(0) extraction in the ICC and suggest a specific colliculo-cochlear feedback for f(0) enhancement.

Recognition of emotional prosody and verbal components of spoken language: an fMRI study

This study examined the neural areas involved in the recognition of both emotional prosody and phonemic components of words expressed in spoken language using echo-planar, functional magnetic resonance imaging (fMRI). Ten right-handed males were asked to discriminate words based on either expressed emotional tone (angry, happy, sad, or neutral) or phonemic characteristics, specifically, initial consonant sound (bower, dower, power, or tower). Significant bilateral activity was observed in the detection of both emotional and verbal aspects of language when compared to baseline activity. We found that the detection of emotion compared with verbal detection resulted in significant activity in the right inferior frontal lobe. Conversely, the detection of verbal stimuli compared with the detection of emotion activated left inferior frontal lobe regions most significantly. Specific analysis of the anterior auditory cortex revealed increased right hemisphere activity during the detection of emotion compared to activity during verbal detection. These findings illustrate bilateral involvement in the detection of emotion in language while concomitantly showing significantly lateralized activity in both emotional and verbal detection, in both the temporal and frontal lobes.

Neural underpinnings of temporal processing: a review of focal lesion, pharmacological, and functional imaging research

The mechanisms by which the brain times events and stores them in memory for later use is increasingly of interest to neuroscientists. There are a variety of neurological disorders in which skilled behaviors are not coordinated and appear less than fluent, which may suggest a disorder in temporal processing. In this review, two influential models are described which suggest timing deficits may be due to impairments in a timekeeping mechanism or various nontemporal processes such as motor implementation, memory, and attention. We then review focal lesion, pharmacological, and functional imaging approaches to understanding the neural underpinnings of temporal processing. Converging findings from these approaches provide support for the role of the basal ganglia in timekeeping operations. Likewise, focal lesion and some functional imaging studies are compatible with a timekeeping role of the cerebellum, though specific regions within the cerebellum that control timing operations have not been identified. In contrast, the results from recent focal lesion research suggests the right middle-frontal and inferior-parietal cortices comprise a pathway that supports attention and working memory operations, which are crucial for timing. Functional imaging data provide some converging evidence for this proposal. Functional imaging work also indicates that a right superior-temporal inferior-frontal pathway sometimes aids timing through subvocal nonlinguistic rehearsal processes. These distributed pathways maintain timekeeping operations in working memory and store representations of temporal events, which is crucial for skilled performance.

Auditory cortex on the human posterior superior temporal gyrus

The human superior temporal cortex plays a critical role in hearing, speech, and language, yet its functional organization is poorly understood. Evoked potentials (EPs) to auditory click-train stimulation presented binaurally were recorded chronically from penetrating electrodes implanted in Heschl's gyrus (HG), from pial-surface electrodes placed on the lateral superior temporal gyrus (STG), or from both simultaneously, in awake humans undergoing surgery for medically intractable epilepsy. The distribution of averaged EPs was restricted to a relatively small area on the lateral surface of the posterior STG. In several cases, there were multiple foci of high amplitude EPs lying along this acoustically active portion of STG. EPs recorded simultaneously from HG and STG differed in their sensitivities to general anesthesia and to changes in rate of stimulus presentation. Results indicate that the acoustically active region on the STG is a separate auditory area, functionally distinct from the HG auditory field(s). We refer to this acoustically sensitive area of the STG as the posterior lateral superior temporal area (PLST). Electrical stimulation of HG resulted in short-latency EPs in an area that overlaps PLST, indicating that PLST receives a corticocortical input, either directly or indirectly, from HG. These physiological findings are in accord with anatomic evidence in humans and in nonhuman primates that the superior temporal cortex contains multiple interconnected auditory areas.

Imaging Cognition II: An Empirical Review of 275 PET and fMRI Studies

Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been extensively used to explore the functional neuroanatomy of cognitive functions. Here we review 275 PET and fMRI studies of attention (sustained, selective, Stroop, orientation, divided), perception (object, face, space/motion, smell), imagery (object, space/ motion), language (written/spoken word recognition, spoken/ no spoken response), working memory (verbal/numeric, object, spatial, problem solving), semantic memory retrieval (categorization, generation), episodic memory encoding (verbal, object, spatial), episodic memory retrieval (verbal, nonverbal, success, effort, mode, context), priming (perceptual, conceptual), and procedural memory (conditioning, motor, and nonmotor skill learning). To identify consistent activation patterns associated with these cognitive operations, data from 412 contrasts were summarized at the level of cortical Brodmann's areas, insula, thalamus, medial-temporal lobe (including hippocampus), basal ganglia, and cerebellum. For perception and imagery, activation patterns included primary and secondary regions in the dorsal and ventral pathways. For attention and working memory, activations were usually found in prefrontal and parietal regions. For language and semantic memory retrieval, typical regions included left prefrontal and temporal regions. For episodic memory encoding, consistently activated regions included left prefrontal and medial-temporal regions. For episodic memory retrieval, activation patterns included prefrontal, medial-temporal, and posterior midline regions. For priming, deactivations in prefrontal (conceptual) or extrastriate (perceptual) regions were consistently seen. For procedural memory, activations were found in motor as well as in non-motor brain areas. Analysis of regional activations across cognitive domains suggested that several brain regions, including the cerebellum, are engaged by a variety of cognitive challenges. These observations are discussed in relation to functional specialization as well as functional integration.

Imaging cognition II: An empirical review of 275 PET and fMRI studies

Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been extensively used to explore the functional neuroanatomy of cognitive functions. Here we review 275 PET and fMRI studies of attention (sustained, selective, Stroop, orientation, divided), perception (object, face, space/motion, smell), imagery (object, space/motion), language (written/spoken word recognition, spoken/no spoken response), working memory (verbal/numeric, object, spatial, problem solving), semantic memory retrieval (categorization, generation), episodic memory encoding (verbal, object, spatial), episodic memory retrieval (verbal, nonverbal, success, effort, mode, context), priming (perceptual, conceptual), and procedural memory (conditioning, motor, and nonmotor skill learning). To identify consistent activation patterns associated with these cognitive operations, data from 412 contrasts were summarized at the level of cortical Brodmann's areas, insula, thalamus, medial-temporal lobe (including hippocampus), basal ganglia, and cerebellum. For perception and imagery, activation patterns included primary and secondary regions in the dorsal and ventral pathways. For attention and working memory, activations were usually found in prefrontal and parietal regions. For language and semantic memory retrieval, typical regions included left prefrontal and temporal regions. For episodic memory encoding, consistently activated regions included left prefrontal and medial temporal regions. For episodic memory retrieval, activation patterns included prefrontal, medial temporal, and posterior midline regions. For priming, deactivations in prefrontal (conceptual) or extrastriate (perceptual) regions were consistently seen. For procedural memory, activations were found in motor as well as in non-motor brain areas. Analysis of regional activations across cognitive domains suggested that several brain regions, including the cerebellum, are engaged by a variety of cognitive challenges. These observations are discussed in relation to functional specialization as well as functional integration.

Auditory attention to space and frequency activates similar cerebral systems

PET was used to test the hypothesis that similar neural systems are involved in attending to spectral and to spatial features of sounds. In each of four conditions subjects heard tones varying randomly in frequency and location and responded to either the low- or the high-frequency stimuli, ignoring location, or to stimuli on the left or right, ignoring frequency. In comparison to a silent baseline, CBF increases were observed in auditory cortex bilaterally and in the right superior parietal, right dorsolateral frontal, and right premotor regions, with no modulation as a function of attentional condition. Analysis of regional covariation indicated a coordinated CBF response between the right parietal region and the right frontal and middle temporal regions. The data imply that auditory attention engages a network of right-hemisphere cortical regions for both spatial location and tonal frequency and support a model whereby auditory attention operates at a level at which separate features have been integrated into a unitary representation.

Musical rhythms in heart period dynamics: a cross-cultural and interdisciplinary approach to cardiac rhythms

The purpose of this study was to expand classic heart period analysis methods by techniques from ethnomusicology that explicitly take complex musical rhythm principles into consideration. The methods used are based on the theory of African music, the theory of symbolic dynamics, and combinatorial theory. Heart period tachograms from 192 24-h electrocardiograms of 96 healthy subjects were transformed into binary symbol sequences that were interpretable as elementary rhythmic (percussive) patterns, the time lines in African music. Using a hierarchical rhythm pattern scheme closely related to the Derler Rhythm Classification (from jazz theory), we calculated the predominance and stability of pattern classes. The results show that during sleep certain classes, specific to individuals, occurred in a cyclically recurrent manner and many times more often than expected. Simultaneously, other classes disappeared more or less completely. Moreover, the most frequent classes obviously originate from phase-locking processes in autonomic regulation (e.g., between respiratory and cardiac cycles). In conclusion, the new interdisciplinary method presented here demonstrates that heart period patterns, in particular those occurring during night sleep, can be interpreted as musical rhythms. This method may be of great potential use in music therapy research.

Positron emission tomography of cortical centers of tinnitus

Tinnitus is associated with a wide variety of disorders in the auditory system. Whether generated peripherally or centrally, tinnitus is believed to be associated with activity in specific cortical regions. The present study tested the hypothesis that these cortical centers subserve the generation, perception and processing of the tinnitus stimulus and that these processes are suppressed by lidocaine and masking. Positron emission tomography was used to map the tinnitus-specific central activity. By subtracting positron emission tomography images of regional cerebral blood flow distribution obtained during suppression of the tinnitus from positron emission tomography images obtained during the habitual tinnitus sensation, we were able to identify brain areas concerned with the cerebral representation of tinnitus. Increased neuronal activity caused by tinnitus occurred predominantly in the right hemisphere with significant foci in the middle frontal and middle temporal gyri, in addition to lateral and mesial posterior sites. The results are consistent with the hypothesis that the sensation of tinnitus is associated with activity in cortical regions functionally linked to subserve attention, emotion and memory. For the first time, the functional anatomy of conditions with and without the habitual tinnitus sensation was obtained and compared in the same subjects.

The role of auditory cortex in retention of rhythmic patterns as studied in patients with temporal lobe removals including Heschl's gyrus

This experiment examined the participation of the auditory cortex of the temporal lobe in the perception and retention of rhythmic patterns. Four patient groups were tested on a paradigm contrasting reproduction of auditory and visual rhythms: those with right or left anterior temporal lobe removals which included Heschl's gyrus (HG), the region of primary auditory cortex (RT-A and LT-A); and patients with right or left anterior temporal lobe removals which did not include HG (RT-a and LT-a). Estimation of lesion extent in HG using an MRI-based probabilistic map indicated that, in the majority of subjects, the lesion was confined to the anterior secondary auditory cortex located on the anterior-lateral extent of HG. On the rhythm reproduction task, RT-A patients were impaired in retention of auditory but not visual rhythms, particularly when accurate reproduction of stimulus durations was required. In contrast, LT-A patients as well as both RT-a and LT-a patients were relatively unimpaired on this task. None of the patient groups was impaired in the ability to make an adequate motor response. Further, they were unimpaired when using a dichotomous response mode, indicating that they were able to adequately differentiate the stimulus durations and, when given an alternative method of encoding, to retain them. Taken together, these results point to a specific role for the right anterior secondary auditory cortex in the retention of a precise analogue representation of auditory tonal patterns.

Functional neuroanatomy of hypnotic state

BACKGROUND

The aim of the present study was to describe the distribution of regional cerebral blood flow during the hypnotic state (HS) in humans, using positron-emission tomography (PET) and statistical parametric mapping.

METHODS

The hypnotic state relied on revivification of pleasant autobiographical memories and was compared to imaging autobiographical material in "normal alertness." A group of 9 subjects under polygraphic monitoring received six H215O infusions and was scanned in the following order: alert-HS-HS-HS with color hallucination-HS with color hallucination-alert. PET data were analyzed using statistical parametric mapping (SPM95).

RESULTS

The group analysis showed that hypnotic state is related to the activation of a widespread, mainly left-sided, set of cortical areas involving occipital, parietal, precentral, premotor, and ventrolateral prefrontal cortices and a few right-sided regions: occipital and anterior cingulate cortices.

CONCLUSIONS

The pattern of activation during hypnotic state differs from those induced in normal subjects by the simple evocation of autobiographical memories. It shares many similarities with mental imagery, from which it differs by the relative deactivation of precuneus.

Learning-induced physiological plasticity in the thalamo-cortical sensory systems: a critical evaluation of receptive field plasticity, map changes and their potential mechanisms

The goal of this review is to give a detailed description of the main results obtained in the field of learning-induced plasticity. The review is focused on receptive field and map changes observed in the auditory, somatosensory and visual thalamo-cortical system as a result of an associative training performed in waking animals. Receptive field (RF) plasticity, 2DG and map changes obtained in the auditory and somatosensory system are reviewed. In the visual system, as there is no RF and map analysis during learning per se, the evidence presented are from increased neuronal responsiveness, and from the effects of perceptual learning in human and non human primates. Across sensory modalities, the re-tuning of neurons to a significant stimulus or map reorganizations in favour of the significant stimuli were observed at the thalamic and/or cortical level. The analysis of the literature in each sensory modality indicates that relationships between learning-induced sensory plasticity and behavioural performance can, or cannot, be found depending on the tasks that were used. The involvement (i) of Hebbian synaptic plasticity in the described neuronal changes and (ii) of neuromodulators as "gating" factors of the neuronal changes, is evaluated. The weakness of the Hebbian schema to explain learning-induced changes and the need to better define what the word "learning" means are stressed. It is suggested that future research should focus on the dynamic of information processing in sensory systems, and the concept of "effective connectivity" should be useful in that matter.

Cerebellar contributions to motor timing: a PET study of auditory and visual rhythm reproduction

The perception and production of temporal patterns, or rhythms, is important for both music and speech. However, the way in which the human brain achieves accurate timing of perceptual input and motor output is as yet little understood. Central control of both motor timing and perceptual timing across modalities has been linked to both the cerebellum and the basal ganglia (BG). The present study was designed to test the hypothesized central control of temporal processing and to examine the roles of the cerebellum, BG, and sensory association areas. In this positron emission tomography (PET) activation paradigm, subjects reproduced rhythms of increasing temporal complexity that were presented separately in the auditory and visual modalities. The results provide support for a supramodal contribution of the lateral cerebellar cortex and cerebellar vermis to the production of a timed motor response, particularly when it is complex and/or novel. The results also give partial support to the involvement of BG structures in motor timing, although this may be more directly related to implementation of the motor response than to timing per se. Finally, sensory association areas and the ventrolateral frontal cortex were found to be involved in modality-specific encoding and retrieval of the temporal stimuli. Taken together, these results point to the participation of a number of neural structures in the production of a timed motor response from an external stimulus. The role of the cerebellum in timing is conceptualized not as a clock or counter but simply as the structure that provides the necessary circuitry for the sensory system to extract temporal information and for the motor system to learn to produce a precisely timed response.

Intensity coding of auditory stimuli: an fMRI study

The effect of stimulus intensity (sound pressure level, SPL) of auditory stimuli on the BOLD response in the auditory cortex was investigated in 14 young and healthy subjects, with no hearing abnormalities, using echo-planar, functional magnetic resonance imaging (fMRI) during a verbal and a non-verbal auditory discrimination task. The stimuli were presented block-wise at three different intensities: 95, 85 and 75 dB (SPL). All subjects showed fMRI signal increases in superior temporal gyrus (STG) covering primary and secondary auditory cortex. Most importantly, the spatial extent of the fMRI response in STG increased with increasing stimulus intensity. It is hypothesized that spreading of excitation is associated with the encoding of increasing stimulus intensity levels. In addition, we found bifrontal activation supposedly evoked by the auditory-articulary loop of working memory. The results presented here should assist in the design of optimal activation strategies for studying the auditory cortex with fMRI paradigms and may help in understanding intensity coding of auditory stimuli.

Functional anatomy of musical processing in listeners with absolute pitch and relative pitch

We used both structural and functional brain imaging techniques to investigate the neural basis of absolute pitch (AP), a specialized skill present in some musicians. By using positron emission tomography, we measured cerebral blood flow during the presentation of musical tones to AP possessors and to control musicians without AP. Listening to musical tones resulted in similar patterns of increased cerebral blood flow in auditory cortical areas in both groups, as expected. The AP group also demonstrated activation of the left posterior dorsolateral frontal cortex, an area thought to be related to learning conditional associations. However, a similar pattern of left dorsolateral frontal activity was also observed in non-AP subjects when they made relative pitch judgments of intervals, such as minor or major. Conversely, activity within the right inferior frontal cortex was observed in control but not in AP subjects during the interval-judgment task, suggesting that AP possessors need not access working memory mechanisms in this task. MRI measures of cortical volume indicated a larger left planum temporale in the AP group, which correlated with performance on an pitch-naming task. Our findings suggest that AP may not be associated with a unique pattern of cerebral activity but rather may depend on the recruitment of a specialized network involved in the retrieval and manipulation of verbal-tonal associations.

Cortical networks underlying mechanisms of time perception

Precise timing of sensory information from multiple sensory streams is essential for many aspects of human perception and action. Animal and human research implicates the basal ganglia and cerebellar systems in timekeeping operations, but investigations into the role of the cerebral cortex have been limited. Individuals with focal left (LHD) or right hemisphere (RHD) lesions and control subjects performed two time perception tasks (duration perception, wherein the standard tone pair interval was 300 or 600 msec) and a frequency perception task, which controlled for deficits in time-independent processes shared by both tasks. When frequency perception deficits were controlled, only patients with RHD showed time perception deficits. Time perception competency was correlated with an independent test of switching nonspatial attention in the RHD but not the LHD patients, despite attention deficits in both groups. Lesion overlays of patients with RHD and impaired timing showed that 100% of the patients with anterior damage had lesions in premotor and prefrontal cortex (Brodmann areas 6, 8, 9, and 46), and 100% with posterior damage had lesions in the inferior parietal cortex. All LHD patients with normal timing had damage in these same regions, whereas few, if any, RHD patients with normal timing had similar lesion distributions. These results implicate a right hemisphere prefrontal-inferior parietal network in timing. Time-dependent attention and working memory functions may contribute to temporal perception deficits observed after damage to this network.

Cytochrome oxidase, acetylcholinesterase, and NADPH-diaphorase staining in human supratemporal and insular cortex: evidence for multiple auditory areas

The pattern of cytochrome oxidase, acetylcholinesterase, and NADPH-diaphorase activity was studied in the supratemporal plane, the posterior part of the superior temporal gyrus, and the insula of normal human brains. Five dark cytochrome oxidase regions were found: (i) on Heschl's gyrus (area TC of von Economo and Koskinas); (ii) on the planum polare (area TC/TG); (iii) posterior to Heschl's gyrus (within area TA); (iv) on the posterior convexity of the superior temporal gyrus (within area TA); and (v) on the posterosuperior insula (area IB). More lightly stained cortex separated these regions (areas IA, TD, and part of TB). The laminar distribution of cytochrome oxidase activity varied in different areas. Acetylcholinesterase-positive fibers predominated in area TC and pyramidal neurons in areas TA and IA and in parts of TB; a mixture of fiber and neuronal staining was found in TC/TG, TD, and IB. NADPH-diaphorase positive profiles included large darkly stained nonpyramidal neurons, mostly in infragranular layers and in subcortical white matter, small faintly stained cells, and a dense array of fibers. The NADPH-diaphorase staining pattern did not vary between areas. The present results suggest that the supratemporal plane, the posterior part of the superior temporal gyrus, and the insula contain at least eight putative cortical areas. Comparison with activation studies by others suggest that, apart from the primary auditory area, six other putative areas may be auditory whereas one putative area, on posterior insula, may be vestibular.

Distributed neural systems underlying the timing of movements

Timing is essential to the execution of skilled movements, yet our knowledge of the neural systems underlying timekeeping operations is limited. Using whole-brain functional magnetic resonance imaging, subjects were imaged while tapping with their right index finger in synchrony with tones that were separated by constant intervals [Synchronization (S)], followed by tapping without the benefit of an auditory cue [Continuation (C)]. Two control conditions followed in which subjects listened to tones and then made pitch discriminations (D). Both the S and the C conditions produced equivalent activation within the left sensorimotor cortex, the right cerebellum (dorsal dentate nucleus), and the right superior temporal gyrus (STG). Only the C condition produced activation of a medial premotor system, including the caudal supplementary motor area (SMA), the left putamen, and the left ventrolateral thalamus. The C condition also activated a region within the right inferior frontal gyrus (IFG), which is functionally interconnected with auditory cortex. Both control conditions produced bilateral activation of the STG, and the D condition also activated the rostral SMA. These results suggest that the internal generation of precisely timed movements is dependent on three interrelated neural systems, one that is involved in explicit timing (putamen, ventrolateral thalamus, SMA), one that mediates auditory sensory memory (IFG, STG), and another that is involved in sensorimotor processing (dorsal dentate nucleus, sensorimotor cortex).

Regional cerebral blood flow changes as a function of delta and spindle activity during slow wave sleep in humans

In the present study, we investigated changes in regional cerebral blood flow (rCBF) in humans during the progression from relaxed wakefulness through slow wave sleep (SWS). These changes were examined as a function of spindle (12-15 Hz) and delta (1.5-4.0 Hz) electroencephalographic (EEG) activity of SWS. rCBF was studied with positron emission tomography (PET) using the H215O bolus method. A maximum of six 60 sec scans were performed per subject during periods of wakefulness and stages 1-4 of SWS, as determined by on-line EEG monitoring. Spectral analysis was performed off-line on the EEG epochs corresponding to the scans for computation of activity in specific frequency bands. The relationship between EEG frequency band activity and normalized rCBF was determined by means of a voxel-by-voxel analysis of covariance. delta activity covaried negatively with rCBF most markedly in the thalamus and also in the brainstem reticular formation, cerebellum, anterior cingulate, and orbitofrontal cortex. After the effect of delta was removed, a significant negative covariation between spindle activity and the residual rCBF was evident in the medial thalamus. These negative covariations may reflect the disfacilitation and active inhibition of thalamocortical relay neurons in association with delta and spindles, as well as the neural substrates underlying the progressive attenuation of sensory awareness, motor responsiveness, and arousal that occur during SWS. delta activity covaried positively with rCBF in the visual and auditory cortex, possibly reflecting processes of dream-like mentation purported to occur during SWS.

Modulation of cerebral blood flow in the human auditory cortex during speech: role of motor-to-sensory discharges

To investigate mechanisms of audio-vocal interactions in the human brain, we studied the effect of speech output on modulation of neuronal activity in the auditory cortex. The modulation was assessed indirectly by measuring changes in cerebral blood flow (CBF) during unvoiced speech (whispering). Using positron emission tomography (PET), CBF was measured in eight volunteers as they uttered syllables at each of seven rates (30, 50, 70, 90, 110, 130 or 150/min) during each of the seven 60-s PET scans. Low-intensity white noise was used throughout scanning to mask auditory input contingent on the whispering. We found that, as a function of the increasing syllable rate, CBF increased in the left primary face area, the upper pons, the left planum temporale and the left posterior perisylvian cortex. The latter two regions contain secondary auditory cortex and previously have been implicated in the processing of speech sounds. We conclude that, in the absence of speech-contingent auditory input, the modulation of CBF in the auditory cortex is mediated by motor-to-sensory discharges. As such, it extends our previous findings of oculomotor corollary discharges to the audio-vocal domain.

The role of subvocalization in auditory imagery

Five experiments explored the utility of subvocal rehearsal, and of an inner-ear/inner-voice partnership, in tasks of auditory imagery. In three tasks (reinterpreting ambiguous auditory images, parsing meaningful letter strings, scanning familiar melodies) subjects relied on a partnership between the inner ear and inner voice, one similar to the phonological loop system described in the short-term memory literature. Apparently subjects subvocally rehearsed the imagery material, which placed the material in a phonological store that allowed the imagery judgement. In a fourth task (distinguishing voiced and unvoiced consonants in imagery), subjects still subvocally rehearsed, but seemed to need no additional phonological store to respond correctly. In this case they may have consulted articulatory or kinesthetic cues instead. In a fifth experiment (making homophone judgements), subjects hardly even needed to subvocally rehearse, a result suggesting that homophone judgements rely on some direct route from print to phonology. We consider the breadth of the partnership between the inner ear and inner voice, the level that subvocal rehearsal occupies in the cognitive system, and the functional neuroanatomy of the phonological loop system.