Biomedical subjects

Jennifer M Rodd

Publications and source records attributed to Jennifer M Rodd.

7 recordsLinked to original sources

PubMed2005

Interleaved silent steady state (ISSS) imaging: a new sparse imaging method applied to auditory fMRI.

The acoustic scanner noise that is generated by rapid gradient switching in echo planar imaging (EPI) is an important confounding factor in auditory fMRI. "Sparse imaging" designs overcome the influence of scanner noise on stimulus presentation by acquiring single brain volumes following a silent stimulus presentation period. However, conventional sparse imaging requires assumptions about the time-to-peak of the evoked hemodynamic response and reduces the amount of EPI data which can be acquired and hence statistical power. In this article, we describe an "interleaved silent steady state" (ISSS) sampling scheme in which we rapidly acquire a set of EPI volumes following each silent stimulus presentation period. We avoid T1-related signal decay during the acquisition of the EPI volumes by maintaining the steady state longitudinal magnetization with a train of silent slice-selective excitation pulses during the silent period, ensuring that signal contrast is constant across successive scans. A validation study comparing ISSS to conventional sparse imaging demonstrates that ISSS imaging provides time course information that is absent in conventional sparse imaging data. The ISSS sequence has a temporal resolution like event-related (ER) imaging within a single trial (unlike conventional sparse imaging, where ER-like temporal resolution can only be achieved by compiling data across many jittered trials of the same stimulus type). This temporal resolution within trials makes ISSS particularly suitable for experiments in which a) scanner noise would interfere with the perception and processing of the stimulus; b) stimuli are several seconds in duration, and activation is expected to evolve and change as the stimulus unfolds; and c) it is impractical to present a single stimulus more than once (for example, repetition priming or familiarity effects would be expected).

Acoustic Stimulation↗

PubMed2005

The neural mechanisms of speech comprehension: fMRI studies of semantic ambiguity.

A number of regions of the temporal and frontal lobes are known to be important for spoken language comprehension, yet we do not have a clear understanding of their functional role(s). In particular, there is considerable disagreement about which brain regions are involved in the semantic aspects of comprehension. Two functional magnetic resonance studies use the phenomenon of semantic ambiguity to identify regions within the fronto-temporal language network that subserve the semantic aspects of spoken language comprehension. Volunteers heard sentences containing ambiguous words (e.g. 'the shell was fired towards the tank') and well-matched low-ambiguity sentences (e.g. 'her secrets were written in her diary'). Although these sentences have similar acoustic, phonological, syntactic and prosodic properties (and were rated as being equally natural), the high-ambiguity sentences require additional processing by those brain regions involved in activating and selecting contextually appropriate word meanings. The ambiguity in these sentences goes largely unnoticed, and yet high-ambiguity sentences produced increased signal in left posterior inferior temporal cortex and inferior frontal gyri bilaterally. Given the ubiquity of semantic ambiguity, we conclude that these brain regions form an important part of the network that is involved in computing the meaning of spoken sentences.

Acoustic Stimulation↗

PubMed2005

Using a hierarchical approach to investigate residual auditory cognition in persistent vegetative state.

Persistent vegetative state is arguably one of the least understood and most ethically troublesome neurological conditions in modern medicine. The term describes a rare disorder in which patients who emerge from coma appear to be awake, but show no signs of awareness. In recent years, a number of studies have demonstrated an important role for functional neuroimaging in the identification of residual cognitive function in patients meeting the clinical criteria for persistent vegetative state. Such studies, when successful, may be particularly useful where there is a concern about the accuracy of the diagnosis and the possibility that residual cognitive function has remained undetected. Unfortunately, functional neuroimaging in persistent vegetative state is extremely complex and subject to numerous methodological, clinical and theoretical difficulties. In this chapter, we argue that in order to most effectively define the degree and extent of preserved cognitive function in persistent vegetative state, a hierarchical approach to cognition is required. To illustrate this point, a series of functional neuroimaging paradigms in the auditory domain are described, which systematically increase in complexity in terms of the auditory and/or linguistic processes required and, therefore, the degree of preserved cognition that can be inferred from "normal" patterns of activation in persistent vegetative patients. Preliminary results in a small series of patients provide a strong basis for the systematic study of possible residual cognitive function in persistent vegetative state.

Auditory Perception↗

PubMed2004

Distinctiveness and correlation in conceptual structure: behavioral and computational studies.

Patients with category-specific deficits have motivated a range of hypotheses about the structure of the conceptual system. One class of models claims that apparent category dissociations emerge from the internal structure of concepts rather than fractionation of the system into separate substores. This account claims that distinctive properties of concepts in the living domain are vulnerable because of their weak correlation with other features. Given the assumption that mutual activation among correlated properties produces faster activation in the normal system, the authors predicted a disadvantage for the distinctive features of living things for unimpaired adults. Results of a speeded feature verification study supported this prediction, as did a computational simulation in which networks mapped from orthography to semantics.

Adolescent↗

PubMed2004

When do leotards get their spots? Semantic activation of lexical neighbors in visual word recognition.

Shadowing and priming studies have provided strong evidence that during spoken word recognition, the meanings of different words that share their onset (e.g., captain and captive) are activated in parallel. In contrast, for visual word recognition, there is little evidence that the meanings of visually similar words are activated in parallel. This is consistent with the idea that for reading (in contrast to listening), since all the sensory information necessary to identify a word is available at once, any competition between visually similar words is resolved before their meanings are retrieved. However, Forster and Hector (2002) have recently shown that for nonwords (e.g., turple), some aspect of the meanings of lexical neighbors (e.g., turtle) can be activated. However, this finding is limited to non-words. The activation of turtle's meaning in response to turple may occur because turple has no meaning. In normal reading, we do not encounter nonwords, and there is strong pressure on the reading system to produce meaningful representations for every word (even misspelled words). The two semantic categorization experiments reported here extend this finding to real words. Participants are slower to decide that leotard is not an animal because of its animal neighbor leopard. This shows that information about a word's meaning can be available before it has been uniquely recognized.

Humans↗

PubMed2004

The effect of semantic ambiguity on reading aloud: a twist in the tale.

Despite numerous studies investigating whether semantic representations are involved in the process of reading aloud, the issue remains controversial. While some studies report significant effects of semantic variables on this task (e.g., Fera, Joordens, Balota, Ferraro, & Besner, 1992; Strain, Patterson, & Seidenberg, 1995), other studies have highlighted possible problems with these studies (e.g., Borowsky & Masson, 1996; Monaghan & Ellis, 2002). The experiments reported here use semantic ambiguity as a marker for semantic involvement and confirm that semantic representations can indeed affect reading aloud, but that the size of semantic effects is influenced by the consistency of the words and the speed with which participants respond.

Humans↗

PubMedDate not supplied

Residual auditory function in persistent vegetative state: a combined PET and fMRI study.

In recent years, a number of studies have demonstrated an important role for functional neuroimaging in the identification of residual cognitive function in persistent vegetative state. Such studies, when successful, may be particularly useful where there is concern about the accuracy of the diagnosis and the possibility that residual cognitive function has remained undetected. Unfortunately, functional neuroimaging in persistent vegetative state is extremely complex and subject to numerous methodological, clinical and theoretical difficulties. Here, we describe the strategy used to study residual auditory and speech processing in a single patient with a clinical diagnosis of persistent vegetative state. Identical positron emission tomography studies, conducted nine months apart, revealed preserved and consistent responses in predicted regions of auditory cortex in response to intelligible speech stimuli. Moreover, a preliminary functional magnetic resonance imaging examination at the time of the second session revealed partially intact responses to semantically ambiguous stimuli, which are known to tap higher aspects of speech comprehension. In spite of the multiple logistic and procedural problems involved, these results have major clinical and theoretical implications and provide a strong basis for the systematic study of possible residual cognitive function in patients diagnosed as being in a persistent vegetative state.

Adult↗