Continuing today, how and where in the brain neural correlates of auditory cognition are formed is an intensive and active area of research. Importantly, our understanding of the role that the cortex plays in hearing has the potential to impact the next generation of cochlear- and brainstem-auditory implants and consequently help those with hearing impairments.
Medicine Otorhinolaryngology. Complements and extends many recent SHAR volumes such as Sound Source Localization Auditory Perception of Sound Sources , and Human Auditory Cortex The neurophysiological data will emphasize the exquisite spatial and temporal resolution of single-neuron Brings together this exciting literature on the neural correlates of auditory cognition see more benefits.
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Show all. Pages However, such a task may also improve word retrieval by increased semantic activation or strengthening of mappings between semantics and phonology [ 1 ]. The neural mechanisms underpinning such effects are not well known in either healthy individuals or those with aphasia. It has been shown that certain aspects of language recovery in aphasia may involve regions also recruited in healthy individuals, for instance during lexical learning [ 2 ]. In fact, it has been proposed that normal priming mechanisms may underlie the successful treatment of word retrieval in aphasia [ 3 ].
A better understanding of these priming mechanisms in unimpaired speakers could aid development of more theoretically driven and neurobiologically informed treatment methods. Therefore, the present study used functional magnetic resonance imaging fMRI to investigate in healthy older adults the effects associated with a commonly used treatment technique on subsequent picture naming performance. The spoken production of a picture name is a complex linguistic operation, requiring integration of perceptual, semantic, phonological and articulatory processes.
Thus the ability to name an object involves multiple, functionally separable, sub-processes. During the semantic stage, successful word production requires the meaning of a picture to be activated within the semantic system, which is a store of word meanings [ 4 ]. Conceptual representations must then be translated into word-level knowledge, by selection of the lexical entry that matches the picture representation.
This abstract lexical unit is given phonetic form during the phonological stage [ 4 ], where the phonological properties of the word are brought together for articulation. A mapping operation must also exist between the semantic and phonological systems, linking word meaning and word form [ 5 ].
Ease of access to the phonological level from the semantic system relies on the strength of these links [ 6 , 7 ]. These three component processes of picture naming i. Word production is supported by a network of perisylvian neural regions involving the frontal, parietal and temporal lobes. It also appears that the semantic and phonological components of single word production engage different regions [ 8 ]. The anterior and mid-portions of the inferior frontal gyrus, the middle and inferior temporal gyri, and the angular gyrus of the parietal lobe have been associated with semantic processing [ 9 — 15 ].
Phonological processing, however, has implicated the posterior portion of the inferior frontal gyrus but see [ 16 ] , the superior temporal gyrus and the supramarginal gyrus of the parietal lobe [ 8 , 9 , 11 , 14 , 17 , 18 ].
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Importantly, our ability to successfully activate, select and produce a specific name can be positively influenced by certain factors. By way of example, two of these intrinsic factors include frequency and age of acquisition. Word frequency refers to the number of times a particular word occurs in spoken or written English and pictures that have names occurring more frequently are named faster than those occurring less frequently [ 19 , 20 ].
The age at which a word was learnt by an individual also influences picture naming latencies, with pictures associated with earlier acquired words recognized and produced faster than later acquired items [ 21 , 22 ] and this effect appears to persist well into older age [ 23 ]. Certain intrinsic properties of words can influence naming performance, however, it is also widely recognized that the simple act of naming a picture once, speeds subsequent naming of that picture [ 24 , 25 ].
This performance enhancement is referred to as priming. A variety of tasks have been used to prime picture naming, including prior instances of phonological processing related to the picture. Contrasting views exist in the behavioral literature, however, regarding the locus of priming using an auditory repetition task.
It has been suggested that this is a phonologically-based task, which facilitates subsequent naming by priming the word form representation, made available during the phonological stage [ 19 ]. Others have proposed that phonological tasks facilitate naming by strengthening the connections between the semantic and phonological levels of processing [ 26 ].
Adding further complexity to this issue, facilitation techniques targeting different components of the naming process appear to have different time courses. It has been proposed that facilitation at the phonological level of processing results in only short-term benefits, while a strengthening of semantic-phonological connections is associated with longer lasting facilitation.
Behavioral evidence for this suggestion was provided by Wheeldon and Monsell [ 26 ] who investigated the effects on picture naming of previously producing the name of an item in response to a definition over the short-term 10 to 35 s or long-term 6 to 12 min. Their results identified strong facilitation over both time frames. They stated that facilitation must have brought about a change in the cognitive pathway shared by both producing a name in response to a definition and naming a picture.
In contrast, a second experiment by the same authors found no facilitation of picture naming 6 to 12 min later from previous production of a homophone of the target item a word that shares pronunciation, but does not share meaning, e. Wheeldon and Monsell [ 26 ] concluded that repeated production of the phonological word form was not sufficient to produce priming effects over long lags. They, therefore, attributed repetition priming effects over a period of minutes to a strengthening of the connections between semantics and phonology, rather than to changes in accessibility of the phonological representation itself.
Implicit memory research generally supports this view by attributing short-term repetition priming effects to a heightened accessibility of lexical representations lasting only a few seconds, whereas longer-lived priming is accounted for by more explicit episodic memory mechanisms [ 27 , 28 ].
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A number of neuroimaging studies have investigated the neural regions engaged by the different component processes of word production by manipulating the phonological or semantic processing involved, often within a repetition priming context. Relevant to the present study is the body of research attempting to identify the brain regions selectively engaged by phonological processing. This research has employed pictures, real words and nonwords in a variety of visual and auditory tasks, including picture naming [ 29 — 32 ], word repetition [ 26 , 33 ], word reading [ 29 , 34 , 35 ], word generation [ 9 , 36 ], word stem completion [ 37 ], word interference [ 38 ], rhyming [ 39 , 40 ], and phoneme or syllable discrimination tasks [ 12 , 39 , 41 ].
Typically these studies, as well as several language-related reviews and meta-analyses [ 8 , 13 , 14 , 42 ], have identified facilitation of subsequent responses associated with a decrease of neural activity in various regions, such as portions of the inferior frontal gyrus, the superior temporal gyrus and the supramarginal gyrus of the parietal lobe. It is evident though, that most research has either simply contrasted tasks involving phonological or semantic processing, compared areas of neural activation engaged by semantic or phonological language tasks relative to some sort of baseline activity [ 42 ], or used the same task on prime and target presentations [ 43 — 45 ].
Few studies have explored repetition priming effects using a specific facilitatory prime task directed at one of the component processes of naming to investigate the longevity of any subsequent effects. In this regard, the majority of repetition priming research investigates effects over short periods, often less than 30 s. The present study considers the facilitation effects of a phonological task over a period of several minutes in the short-term , and over a period of days in the long-term which may be indicative of a stable and more enduring change in processing [ 31 , 46 ].
Two neuroimaging studies have explored the neural mechanisms mediating very long-lasting facilitation of picture naming. In a study by van Turennout et al. Subjects were asked to name objects aloud during prime presentations, but during the scanning session were required to silently name each item, such that task compliance and reaction times could not be measured.
A decrease of activity for multiple exposures to stimuli was found in bilateral occipitotemporal regions and left inferior frontal cortices, as well as an increase in activity in the left anterior insula and left basal ganglia [ 30 ]. This activity was time dependent in the inferior frontal cortex, with larger decreases in activity when more time intervened between successive exposures [ 30 ]. The authors suggest this finding is consistent with experience-related changes in activity, resulting in less effort being required to encode and identify a repeated object name [ 47 ] in posterior regions and the existence of a procedural learning mechanism in more anterior regions, as well as the basal ganglia and insula cortex [ 30 ].
Meister et al. An overt naming task was employed in pre-scan sessions and a covert naming task was employed during scanning.
Behavioral picture priming effects were associated with reduced activity in the posterior inferior temporal cortex and the anterior inferior frontal region for both short-term one day and long-term 6 weeks intervals [ 31 ]. Although both studies found priming-related mechanisms in neural regions associated with naming over a period of weeks [ 30 , 31 ], it is difficult to determine which components of the word production process are contributing to these long lasting priming effects. This is due to the fact that any one, or combination, of the different levels of word production could be contributing to the neural changes resulting from repetition priming when a picture naming task is used at prime presentation and during scanning.
The present experiment builds upon this previous work in a significant way by requiring participants to produce overt picture naming responses within the fMRI scanning session and, importantly, by utilizing a different task on prime presentation. An auditory repetition task was used to target the phonological component of naming, and allowed investigation of the longevity of any facilitation effects upon subsequent picture naming which may arise from this specific aspect of word production over a period of days.
In an effort to build upon previous research and discriminate between competing claims regarding the basis and longevity of repetition priming, the present study used fMRI to investigate the neurocognitive substrates underlying facilitation of word retrieval by a phonological technique. The auditory repetition task utilized in this study was performed in the presence of a picture and was used to facilitate subsequent overt naming of the same picture over long within days and short within minutes time frames.
Importantly, the three main naming conditions of interest were presented in a single scanning session. It was hypothesized that any short-term facilitation effects should primarily engage regions associated with phonological processing, indicative of the fact that temporary facilitation may be occurring at the phonological level of processing. On the basis of previous neuroimaging research [ 8 , 13 — 15 , 42 ] we expected these areas to include the posterior portions of the inferior frontal and superior temporal gyri, and the supramarginal gyrus of the parietal lobe.
Additionally, we hypothesized that long-term facilitation could involve brain areas linked to both semantic and phonological processing, which would suggest that the longevity of facilitation from a phonological task relies on a strengthening of the connections between semantic and phonological levels of processing. These semantic regions, in addition to areas associated with phonological processing, include the anterior portion of the inferior frontal gyrus, the middle and inferior temporal gyri, the angular gyrus of the parietal lobe, and possibly regions linked to episodic memory [ 8 , 13 — 15 , 42 ].
Twenty-one 12 female healthy older adults average age The average educational level of participants was Participants received no direct financial benefit, but were reimbursed for travel costs. All were right handed, had normal or corrected to normal vision and were native speakers of English.
Exclusionary criteria included significant hearing loss identified by pure tone audiometry screening , any neurological disease or disorder, mental illness, a history of alcohol abuse, as well as the presence of any metal objects within the body, or other contraindications for magnetic resonance imaging.
In addition, participants were tested for visual acuity, screened for cognitive impairment with the Mini-Mental State Examination [ 48 ] and for depression with the Geriatric Depression Scale [ 49 ]. Full ethical approval was obtained from the University of Queensland Medical Research Ethics Committee and written informed consent obtained from each participant in accordance with the Declaration of Helsinki.
The images were grey-scaled with an average luminance of Mean reaction times and percentage name agreement data was obtained from the International Picture Naming Project database [ 50 ]. Frequency counts were sourced from the CELEX lexical database [ 51 ] and age of acquisition norms from Morrison et al. Associated imageability ratings were obtained from the Medical Research Council psycholinguistic database [ 52 ].
The 60 stimuli were divided into three sets of 20 items, with each set assigned to a different main condition of interest - unfacilitated, short-term facilitated or long-term facilitated. Assignment of sets to conditions was counterbalanced across participants. Additionally, no stimuli items within a set were first associates of each other, as determined by the Edinburgh Associative Thesaurus [ 53 ].
The auditory stimuli associated with pictures were spoken by a female voice and digitally recorded at Hz, mono, 32 bit, in a sound-proof recording studio. A summary of the presentation of randomized stimuli. Facilitation phase : one set of 20 pictures were presented three times on two separate occasions six times total , simultaneously with their auditory names, for repetition LT prime. Testing phase during scan : the long-term facilitated set were presented again for naming LT target ; a set of 20 pictures were presented twice - once as a prime along with the auditory name for repetition ST prime and then presented again 6 to 12 trials later for naming ST target ; and one set of 20 unfacilitated pictures were also presented once for naming UN , along with an additional set of 20 unfacilitated non-critical fillers.
The second phase testing phase was performed during an fMRI scanning session, with all three sets of stimulus items presented, plus an additional 20 items as non-critical fillers for naming. The behavioral task for the testing phase was created using Microsoft Visual Basic 6. Each trial lasted This was followed by a blank screen for 9. The long-term facilitation set of items, which were previously presented during the facilitation sessions, were presented again in the scanner to investigate any long-term facilitation effects with no more than two days between the final facilitation session and scan.
The short-term facilitation set of items were presented twice within the scanner in different random order : once as a prime, along with the auditory name of that item, for overt repetition by participants and then presented again as a target within a lag of 6 to 12 trials, average 10 trials for naming to investigate any short-term facilitation effects over a period of no more than 3 min. A set of unfacilitated items were also presented once within the scanner as a baseline for comparison purposes.
Stimuli were presented pseudo-randomly in blocks of five trials per condition long-term facilitated condition, short-term facilitated prime and target conditions, and unfacilitated condition , interspersed across the course of the scanning session. Stimuli were presented in blocks so that participants could be prepared for each type of task and thereby minimize any effects of constant task switching. In this regard, at the commencement of each trial block of five items, either the word "Name" for main naming conditions of interest and filler items or the word "Repeat" for short-term facilitated prime items was displayed in the centre of the screen to provide task instructions to participants.
The system utilized a transverse electromagnetic head coil [ 55 ] to enhance imaging resolution at a high field strength. To obtain minimal scanner noise during picture presentation and response time 4. For the following This design was primarily utilized to avoid artefacts associated with any head movement during an overt response.
The design also allowed participants to hear auditorily presented stimuli, and permitted the recording of overt responses and accurate reaction times [ 56 , 57 ]. A total of GE-EPI volumes were acquired over three runs, with the first five volumes the first A point-spread function PSF mapping sequence was acquired prior to GE-EPI acquisitions, allowing the distortion in geometry and intensity to be corrected in the time series data [ 58 ]. Incorrect responses and naming trials which elicited no response from participants 4. During spatial pre-processing the image time series were first realigned using rigid body motion correction with INRIAlign [ 59 ].
The mean EPI image generated from the realigned series for each participant was coregistered with the T 1 image acquired in the same session. These transformations were applied to the realigned EPI time series. Due to the partial collection of hemodynamic response function, a factor of the behavioral interleaved gradient design, a general linear model GLM for the fMRI time series was constructed using finite impulse response functions.
Specific hypothesis-driven regions of interest ROIs were based upon the findings of various language-related meta-analyses, including Vigneau et al. Three ROIs were identified as having been previously associated with phonological processing, including the posterior region of the inferior frontal gyrus pars opercularis , 12, 20 , the posterior portion of the superior temporal gyrus , , 12 and the supramarginal gyrus of the parietal lobe , , Additionally, six ROIs associated with semantic processing were selected within the anterior pars orbitalis and mid pars triangularis portions of the inferior frontal gyrus , 31, -9; , 20, 4 , the anterior superior temporal gyrus , , -5 , the mid-section of the middle temporal gyrus , , 1 , the posterior inferior temporal gyrus , ,-7 , and the angular gyrus of the parietal lobe , , Therefore, these two spherical ROIs may extend somewhat into the middle superior temporal region in the case of the posterior superior temporal gyrus and into the posterior middle temporal region for the mid-section of the middle temporal gyrus.
Timbre: Acoustics, Perception, and Cognition
Corrected p -values were calculated with the function "p. Whole brain analyses were also conducted, with the neuroanatomical location of peak maxima identified using automated anatomical labelling software [ 63 ]. Phonological facilitation effects in behavioral data. Error bars indicate standard error mean.
A , Mean reaction times and standard errors for each condition.
B , Mean percentage accuracy for each condition. Region of interest analysis. Bar graph indicates relative mean percentage BOLD signal change as a function of facilitation, compared to the unfacilitated condition. Whole brain analyses. The aim of this study was to investigate the short- and long-term facilitation of overt picture naming using an auditory repetition task, in order to determine the neurocognitive substrates underlying facilitation from phonological tasks over time in healthy aging adults.
It was hypothesized that short-term facilitation effects should engage regions associated with phonological processing, and that long-term facilitation may involve brain areas linked to both semantic and phonological processing. The present study found that long-term facilitation was indeed driven by modulation of activity in regions associated with both phonological left posterior superior temporal gyrus and semantic processing left middle temporal gyrus.
Original Research ARTICLE
However, short-term facilitation was primarily associated with decreased activity in an area known to be involved in semantic processing and object recognition left occipitotemporal region. Modulation of activity in areas associated with semantic processing may be due to the fact that both semantic and phonological processing occur to some degree with most language-related tasks [ 1 ].
In other words, although an auditory repetition task can be conceived as phonological, particularly when given as a treatment of word retrieval deficits in aphasia, it also involves semantic processing mechanisms. This is particularly the case when the picture is presented at the same time as the auditory word form and the speaker is assumed to understand the word being repeated.
The behavioral results see Figure 2 showed that both short-term and long-term facilitated items were named significantly faster than unfacilitated items, with a larger priming effect for short-term as compared to long-term items. A similar pattern of priming was revealed in the accuracy data, with short-term and long-term facilitated items named significantly more accurately than unfacilitated items. The presence of these behavioral priming effects indicates that repeating auditorily presented stimuli can facilitate subsequent picture naming in healthy older adults and that the magnitude of this effect is reduced over time.
Neuroimaging results revealed decreased activity for facilitated conditions in both phonological and semantic regions, which could be attributed to "repetition suppression" - a relative decrease in cortical activity following repeated presentation of a stimulus, reflecting greater processing efficiency [ 30 , 47 , 65 — 68 ]. In addition, there was increased activity for short-term facilitated items in a neural region previously linked to phonological processing.
This may reflect "repetition enhancement" - an increase in activity, which is often associated with additional processing upon repeated stimulus presentation [ 30 , 65 ]. We now turn to a discussion of findings, firstly in terms of neural regions where repetition suppression effects for facilitated items were identified and, secondly, areas where repetition enhancement effects for facilitated items were shown. Decreased activation for facilitated items was identified in three temporal regions: the superior, middle and inferior temporal gyri.
This finding is largely consistent with previous picture naming studies investigating long lasting facilitation of naming, which have documented a decrease in activity for previously encountered items in occipitotemporal regions [ 30 ] and the posterior inferior temporal gyrus [ 31 ].
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In the current investigation, both the ROI and whole brain analyses revealed a decrease in activity for long-term facilitated items relative to short-term facilitated items in the superior temporal gyrus, an area linked to phonological processing. More specifically, the superior temporal region is known to be involved in phonological access [ 13 , 33 , 69 ]. A repetition suppression effect here suggests that long-term facilitation may have resulted in more efficient activation and retrieval of phonological representations.
Both analyses also identified decreases in activation for short-term facilitated items relative to unfacilitated items in the inferior temporal region. The ROI analyses showed this decrease in activity within the posterior inferior temporal gyrus and the whole brain analyses identified a reduction in activity in the left inferior occipital gyrus, extending to the inferior temporal gyrus.
In addition, the whole brain analyses identified a decrease in activation for long-term facilitated items when compared to unfacilitated items in the middle temporal gyrus. Both the middle and inferior temporal gyri are thought to be involved in lexical selection, where the lexical entry that matches a picture representation is accessed and selected [ 8 , 10 , 70 , 71 ]. Therefore, this decrease in activity for long-term facilitated items in the middle temporal region and for short-term facilitated items in the inferior temporal region, may be attributable to repeated and more efficient lexical selection of these previously presented items.
It should be pointed out that, contrary to our original hypothesis regarding short-term effects primarily engaging regions associated with phonological processing, the most significant result within the ROI analyses was a decrease in activity for short-term facilitated items in the posterior inferior temporal gyrus refer to Figure 3.
As previously noted, although our facilitation task attempted to focus on phonological processing, it could be the obligatory semantic aspects of the task i. Additionally, object priming studies commonly report decreases in activation within occipitotemporal regions [ 30 , 31 , 46 , 72 ].