Attention Mobilization as a Modulator of Listening Effort: Evidence From Pupillometry.

Listening to speech in noise can require substantial mental effort, even among younger normal-hearing adults. The task-evoked pupil response (TEPR) has been shown to track the increased effort exerted to recognize words or sentences in increasing noise. However, few studies have examined the trajectory of listening effort across longer, more natural, stretches of speech, or the extent to which expectations about upcoming listening difficulty modulate the TEPR. Seventeen younger normal-hearing adults listened to 60-s-long audiobook passages, repeated three times in a row, at two different signal-to-noise ratios (SNRs) while pupil size was recorded. There was a significant interaction between SNR, repetition, and baseline pupil size on sustained listening effort. At lower baseline pupil sizes, potentially reflecting lower attention mobilization, TEPRs were more sustained in the harder SNR condition, particularly when attention mobilization remained low by the third presentation. At intermediate baseline pupil sizes, differences between conditions were largely absent, suggesting these listeners had optimally mobilized their attention for both SNRs. Lastly, at higher baseline pupil sizes, potentially reflecting overmobilization of attention, the effect of SNR was initially reversed for the second and third presentations: participants initially appeared to disengage in the harder SNR condition, resulting in reduced TEPRs that recovered in the second half of the story. Together, these findings suggest that the unfolding of listening effort over time depends critically on the extent to which individuals have successfully mobilized their attention in anticipation of difficult listening conditions.

Neural Dynamics of the Processing of Speech Features: Evidence for a Progression of Features from Acoustic to Sentential Processing.

When we listen to speech, our brain's neurophysiological responses "track" its acoustic features, but it is less well understood how these auditory responses are modulated by linguistic content. Here, we recorded magnetoencephalography (MEG) responses while subjects listened to four types of continuous-speech-like passages: speech-envelope modulated noise, English-like non-words, scrambled words, and narrative passage. Temporal response function (TRF) analysis provides strong neural evidence for the emergent features of speech processing in cortex, from acoustics to higher-level linguistics, as incremental steps in neural speech processing. Critically, we show a stepwise hierarchical progression of progressively higher order features over time, reflected in both bottom-up (early) and top-down (late) processing stages. Linguistically driven top-down mechanisms take the form of late N400-like responses, suggesting a central role of predictive coding mechanisms at multiple levels. As expected, the neural processing of lower-level acoustic feature responses is bilateral or right lateralized, with left lateralization emerging only for lexical-semantic features. Finally, our results identify potential neural markers of the computations underlying speech perception and comprehension.

Neural tracking measures of speech intelligibility: Manipulating intelligibility while keeping acoustics unchanged.

Neural speech tracking has advanced our understanding of how our brains rapidly map an acoustic speech signal onto linguistic representations and ultimately meaning. It remains unclear, however, how speech intelligibility is related to the corresponding neural responses. Many studies addressing this question vary the level of intelligibility by manipulating the acoustic waveform, but this makes it difficult to cleanly disentangle the effects of intelligibility from underlying acoustical confounds. Here, using magnetoencephalography recordings, we study neural measures of speech intelligibility by manipulating intelligibility while keeping the acoustics strictly unchanged. Acoustically identical degraded speech stimuli (three-band noise-vocoded, ~20 s duration) are presented twice, but the second presentation is preceded by the original (nondegraded) version of the speech. This intermediate priming, which generates a "pop-out" percept, substantially improves the intelligibility of the second degraded speech passage. We investigate how intelligibility and acoustical structure affect acoustic and linguistic neural representations using multivariate temporal response functions (mTRFs). As expected, behavioral results confirm that perceived speech clarity is improved by priming. mTRFs analysis reveals that auditory (speech envelope and envelope onset) neural representations are not affected by priming but only by the acoustics of the stimuli (bottom-up driven). Critically, our findings suggest that segmentation of sounds into words emerges with better speech intelligibility, and most strongly at the later (~400 ms latency) word processing stage, in prefrontal cortex, in line with engagement of top-down mechanisms associated with priming. Taken together, our results show that word representations may provide some objective measures of speech comprehension.

Neural Tracking Measures of Speech Intelligibility: Manipulating Intelligibility while Keeping Acoustics Unchanged.

Neural speech tracking has advanced our understanding of how our brains rapidly map an acoustic speech signal onto linguistic representations and ultimately meaning. It remains unclear, however, how speech intelligibility is related to the corresponding neural responses. Many studies addressing this question vary the level of intelligibility by manipulating the acoustic waveform, but this makes it difficult to cleanly disentangle effects of intelligibility from underlying acoustical confounds. Here, using magnetoencephalography (MEG) recordings, we study neural measures of speech intelligibility by manipulating intelligibility while keeping the acoustics strictly unchanged. Acoustically identical degraded speech stimuli (three-band noise vocoded, ~20 s duration) are presented twice, but the second presentation is preceded by the original (non-degraded) version of the speech. This intermediate priming, which generates a 'pop-out' percept, substantially improves the intelligibility of the second degraded speech passage. We investigate how intelligibility and acoustical structure affects acoustic and linguistic neural representations using multivariate Temporal Response Functions (mTRFs). As expected, behavioral results confirm that perceived speech clarity is improved by priming. TRF analysis reveals that auditory (speech envelope and envelope onset) neural representations are not affected by priming, but only by the acoustics of the stimuli (bottom-up driven). Critically, our findings suggest that segmentation of sounds into words emerges with better speech intelligibility, and most strongly at the later (~400 ms latency) word processing stage, in prefrontal cortex (PFC), in line with engagement of top-down mechanisms associated with priming. Taken together, our results show that word representations may provide some objective measures of speech comprehension.

Effects of aging on cortical representations of continuous speech.

Understanding speech in a noisy environment is crucial in day-to-day interactions and yet becomes more challenging with age, even for healthy aging. Age-related changes in the neural mechanisms that enable speech-in-noise listening have been investigated previously; however, the extent to which age affects the timing and fidelity of encoding of target and interfering speech streams is not well understood. Using magnetoencephalography (MEG), we investigated how continuous speech is represented in auditory cortex in the presence of interfering speech in younger and older adults. Cortical representations were obtained from neural responses that time-locked to the speech envelopes with speech envelope reconstruction and temporal response functions (TRFs). TRFs showed three prominent peaks corresponding to auditory cortical processing stages: early (∼50 ms), middle (∼100 ms), and late (∼200 ms). Older adults showed exaggerated speech envelope representations compared with younger adults. Temporal analysis revealed both that the age-related exaggeration starts as early as ∼50 ms and that older adults needed a substantially longer integration time window to achieve their better reconstruction of the speech envelope. As expected, with increased speech masking envelope reconstruction for the attended talker decreased and all three TRF peaks were delayed, with aging contributing additionally to the reduction. Interestingly, for older adults the late peak was delayed, suggesting that this late peak may receive contributions from multiple sources. Together these results suggest that there are several mechanisms at play compensating for age-related temporal processing deficits at several stages but which are not able to fully reestablish unimpaired speech perception.NEW & NOTEWORTHY We observed age-related changes in cortical temporal processing of continuous speech that may be related to older adults' difficulty in understanding speech in noise. These changes occur in both timing and strength of the speech representations at different cortical processing stages and depend on both noise condition and selective attention. Critically, their dependence on noise condition changes dramatically among the early, middle, and late cortical processing stages, underscoring how aging differentially affects these stages.

NLGC: Network localized Granger causality with application to MEG directional functional connectivity analysis.

Identifying the directed connectivity that underlie networked activity between different cortical areas is critical for understanding the neural mechanisms behind sensory processing. Granger causality (GC) is widely used for this purpose in functional magnetic resonance imaging analysis, but there the temporal resolution is low, making it difficult to capture the millisecond-scale interactions underlying sensory processing. Magnetoencephalography (MEG) has millisecond resolution, but only provides low-dimensional sensor-level linear mixtures of neural sources, which makes GC inference challenging. Conventional methods proceed in two stages: First, cortical sources are estimated from MEG using a source localization technique, followed by GC inference among the estimated sources. However, the spatiotemporal biases in estimating sources propagate into the subsequent GC analysis stage, may result in both false alarms and missing true GC links. Here, we introduce the Network Localized Granger Causality (NLGC) inference paradigm, which models the source dynamics as latent sparse multivariate autoregressive processes and estimates their parameters directly from the MEG measurements, integrated with source localization, and employs the resulting parameter estimates to produce a precise statistical characterization of the detected GC links. We offer several theoretical and algorithmic innovations within NLGC and further examine its utility via comprehensive simulations and application to MEG data from an auditory task involving tone processing from both younger and older participants. Our simulation studies reveal that NLGC is markedly robust with respect to model mismatch, network size, and low signal-to-noise ratio, whereas the conventional two-stage methods result in high false alarms and mis-detections. We also demonstrate the advantages of NLGC in revealing the cortical network-level characterization of neural activity during tone processing and resting state by delineating task- and age-related connectivity changes.

Sharps injuries among medical students in the Faculty of Medicine, Colombo, Sri Lanka.

INTRODUCTION: Medical students undertake clinical procedures which carry a risk of sharps injuries exposing them to bloodborne infections. OBJECTIVES: To study the prevalence and correlates of sharps injuries among 4th-year medical students in the Faculty of Medicine, University of Colombo, Sri Lanka. MATERIALS AND METHODS: The survey was conducted among 4th-year medical students to find out the incidence of injuries during high-risk procedures, associated factors and practice and perceptions regarding standard precautions. A self-administered questionnaire was administered to a batch of 197 4th-year medical students. RESULTS: A total of 168 medical students responded. One or more injury was experienced by 95% (N = 159) of the students. The majority (89%) occurred during suturing; 23% during venipuncture and 14% while assisting in deliveries. Most of the incidents (49%) occurred during Obstetrics and Gynecology attachments. Recapping needles led to 8.6% of the injuries. Thirty-five percent of students believed they were inadequately protected. In this group, adequate protection was not available in 21% of the incidences and 24% thought protection was not needed. Following the injury, 47% completely ignored the event and only 5.7% followed the accepted post-exposure management. Only 34% of the students knew about post-exposure management at the time of the incident. Only 15% stated that their knowledge regarding prevention and management was adequate. The majority (97%) believed that curriculum should put more emphasis on improving the knowledge and practice regarding sharps injuries. CONCLUSIONS: The incidence of sharps injuries was high in this setting. Safer methods of suturing should be taught and practiced. The practice of standard precautions and post-injury management should be taught.

Are tsunami survivors satisfied with the provision and quality of healthcare they received?

The objective of this study is to evaluate the perceptions of Internally Displaced Persons (IDPs) in tsunami relief camps on provision and quality of health care services, during the aftermath of the disaster. A randomly selected health administrative area in the Southern Province of Sri Lanka is selected. Two approaches using both quantitative and qualitative methods. The study assessed the perceptions of IDPs regarding on provision and quality of health care facilities, using an interviewer administered questionnaire (survey) in 200 family units. In-depth interviews were conducted with IDPs and relevant health authorities. A majority (88%) of the people was satisfied with the immediate medical assistance. However 48% of IDPs and authorities felt that frequency of visits paid by medical teams have decreased over time. Fifty-three percent were dissatisfied with the toilet facilities provided. A majority was satisfied with health education (82%) and supply of drinking water (80%). Tsunami survivors felt that health services provided during the intermediate phase was unsatisfactory compared to the immediate phase. We recommend attention to ensuring ongoing access to health care and to improving the sanitary facilities in the camps.

Students' perception of problem-based learning in the medical curriculum of the Faculty of Medicine, University of Colombo.

INTRODUCTION: Problem-based learning (PBL) is used as an instructional method in the system-based modules of the new innovative curriculum of the Colombo Medical Faculty in Sri Lanka. This study was undertaken to assess whether objectives of having PBL to facilitate acquisition of desirable learning skills and generic skills had been achieved. The perceived advantages and disadvantages of PBL were also studied. MATERIALS AND METHODS: The study population comprised third year medical students who had completed 12 PBL sessions. A self-administered questionnaire, which measured learning outcomes and acquisition of generic skills on a 5-point Likert rating scale, was used. RESULTS: The response rate was 87.2% (n = 188). Eighty per cent of students were aware of the rationale for having PBL and of learning from recommended material. Seventy-five per cent knew the competencies that could be acquired from PBL and two-thirds knew about the importance of small group discussions. PBL had helped to improve communication skills in 57% and problem solving skills in 52%. The main disadvantage was that it was time-consuming. Only 46.6% were satisfied with the participation of colleagues in the group. Seventy-six per cent felt that PBL could be better conducted. CONCLUSION: Awareness of concepts of PBL, reasons for its inclusion in the curriculum and educational advantage was high. The main disadvantage perceived was that it was time-consuming. There is a need to improve the conduct of PBL and, provide guidance and awareness programme for students.