Short-term Memory Processes Research Articles

Fractional calculus derivation of a rate-dependent PPR-based cohesive fracture model: theory, implementation, and numerical results

Rate-dependent fracture has been extensively studied using cohesive zone models (CZMs). Some of them use classical viscoelastic material models based on springs and dashpots. However, such viscoelastic models, characterized by relaxation functions with exponential decay, are inadequate to simulate fracture for a wide range of loading rates. To improve the accuracy of existing models, this work presents a mixed-mode rate-dependent CZM that combines the features of the Park–Paulino–Roesler (PPR) cohesive model and a fractional viscoelastic model. This type of viscoelastic model uses differential operators of non-integer order, leading to power-law-type relaxation functions with algebraic decay. We derive the model in the context of damage mechanics, such that undamaged viscoelastic tractions obtained from a fractional viscoelastic model are scaled using two damage parameters. We obtain these parameters from the PPR cohesive model and enforce them to increase monotonically during the entire loading history, which avoids artificial self-healing. We present three examples, two used for validation purposes and one to elucidate the physical meaning of the fractional differential operators. We show that the model is able to predict rate-dependent fracture process of rubber-like materials for a wide range of loading rates and that it can capture rate-dependent mixed-mode fracture processes accurately. Results from the last example indicate that the order of the fractional differential operators acts as a memory-like parameter that allows for the fracture modeling of long- and short-term memory processes. The ability of fractional viscoelastic models to model this type of process suggests that relaxation functions with algebraic decay lead to accurate fracture modeling of materials for a wide range of loading rates.

An essential role of the mouse synapse-associated protein Syap1 in circuits for spontaneous motor activity and rotarod balance.

ABSTRACTSynapse-associated protein 1 (Syap1) is the mammalian homologue of synapse-associated protein of 47 kDa (Sap47) in Drosophila. Genetic deletion of Sap47 leads to deficiencies in short-term plasticity and associative memory processing in flies. In mice, Syap1 is prominently expressed in the nervous system, but its function is still unclear. We have generated Syap1 knockout mice and tested motor behaviour and memory. These mice are viable and fertile but display distinct deficiencies in motor behaviour. Locomotor activity specifically appears to be reduced in early phases when voluntary movement is initiated. On the rotarod, a more demanding motor test involving control by sensory feedback, Syap1-deficient mice dramatically fail to adapt to accelerated speed or to a change in rotation direction. Syap1 is highly expressed in cerebellar Purkinje cells and cerebellar nuclei. Thus, this distinct motor phenotype could be due to a so-far unknown function of Syap1 in cerebellar sensorimotor control. The observed motor defects are highly specific since other tests in the modified SHIRPA exam, as well as cognitive tasks like novel object recognition, Pavlovian fear conditioning, anxiety-like behaviour in open field dark-light transition and elevated plus maze do not appear to be affected in Syap1 knockout mice.

Accounting for individual differences in the development of verbal and visual short term memory processes in children

In developmental research on memory, the model of working memory of Baddeley and Hitch (1974, Baddeley, 1986) is the theory most often referred to. This theory has played an important role in studies on human learning in general. However, it is not clear how the verbal and visual short term memory systems develop. In order to investigate this development, we argue that some important issues should be taken into account; a longitudinal research design and individual differences between children. The current study is a follow-up study in which we investigated the transitions that a subsample of 30 children made between verbal and visual processing during the course of one year. Our results showed that the children showed large variation in STM processes and did not move from one type of processing to another in a consistent manner. This implies that the development of the verbal and visual STM systems may be less predictable than expected based on the literature, stressing the importance to be cautious when individual differences between children are not taken into account.

Memory and exploratory behavior impairment in ovariectomized Wistar rats

BackgroundEstrogen deficiency is linked to changes in several physiological processes, but the extent to which it associates with cognitive changes in menopause context is controversial.RationaleWe evaluated the impact of ovariectomy on memory processes and normal exploratory behavior in Wistar rats.MethodsYoung adult rats (4–6 months) were either ovariectomized (OVX group) (N = 10), sham operated (N = 10), or untouched (naïve controls) (N = 8). Afterwards, they were monitored for 12 weeks during which their cognitive functions were evaluated at first week (S1), second (S2), every 3 weeks (S5, S8) and then at week 12 (S12) using: (i) object recognition test to evaluate the short-term and long-term non-spatial memory; (ii) the object placement test to assess the spatial memory; and (iii) normal exploratory behavior components like locomotor and vertical activities in an open field arena.ResultsMarked changes in ovariectomized rats were observed in long-term non-spatial memory (~ 40% change vs. naïve and sham, P < 0.001) and spatial memory (~ 30% change, P < 0.05) from S2. Instead, from S5 the exploratory behavior was affected, with decreases in line crossing and rearing episode numbers (~ 40% change, P < 0.01), and in the time spent in the center of open field arena (~ 60% change, P < 0.01).ConclusionsOur findings support the involvement of sex hormones in cognitive functions in female rats and suggest that controversy on the importance of cognitive affections in menopause context may emerge from differences between short-term and long-term memory processes.

Exploring Cognitive Concomitants of Mental Fatigue in Patients with Coronary Artery Disease

Objective: Fatigue and reduced exercise capacity are common concomitants of coronary artery disease (CAD). They are known to be associated with the deterioration in mental health, including emotional and cognitive status. However, the precise nature of the inter-relationship is poorly understood. The aim of this study was to investigate the relationship between fatigue and exercise capacity on the one hand and changes in cognitive functioning on the other, to generate new heuristics for clinical management and outcome prediction of CAD. Methods: A cross-sectional study included 827 in-patients (58 ± 9 years, 75% men) with CAD. Patients were evaluated for demographic, cardiac characteristics, and exercise capacity. The Multidimensional Fatigue Inventory-20 was used to assess fatigue, the Mini Mental State Examination for global cognitive function, the Digit Span Test, Digit Symbol Test, and Trail Making Test for executive aspects of cognitive functioning, and the Hospital Anxiety and Depression Scale for anxiety and depression symptom severity. Results: Using multiple regression analysis, after adjusting for possible confounders such as anxiety and depression, mental fatigue was associated with several executive aspects of cognitive function including short-term memory (Digit Symbol Test pairs recalled correctly [β = –0.127, p < 0.005]), psychomotor performance (time to complete the Digit Symbol Test [β = 0.089, p < 0.03]), and cognitive processing speed (Trail Making Test A [β = 0.081, p < 0.05]). Conclusion: In rehabilitating CAD patients, certain aspects of executive functioning were independently associated with mental fatigue. These findings suggest that the subjective experience of mental fatigue, rather than reduced exercise capacity, is significantly associated with cognitive function.

Feature-Based Visual Short-Term Memory Is Widely Distributed and Hierarchically Organized

Feature-based visual short-term memory is known to engage both sensory and association cortices. However, the extent of the participating circuit and the neural mechanisms underlying memory maintenance is still a matter of vigorous debate. To address these questions, we recorded neuronal activity from 42 cortical areas in monkeys performing a feature-based visual short-term memory task and an interleaved fixation task. We find that task-dependent differences in firing rates are widely distributed throughout the cortex, while stimulus-specific changes in firing rates are more restricted and hierarchically organized. We also show that microsaccades during the memory delay encode the stimuli held in memory and that units modulated by microsaccades are more likely to exhibit stimulus specificity, suggesting that eye movements contribute to visual short-term memory processes. These results support a framework in which most cortical areas, within a modality, contribute to mnemonic representations at timescales that increase along the cortical hierarchy.

Executive dysfunction in patients with spinocerebellar ataxia type 3.

The aim of this study was to assess the cognitive functions of patients with spinocerebellar ataxia type 3(SCA3). We examined 15 patients with genetically confirmed SCA3 and 15 healthy control subjects matched for age, years of education, and intellectual ability. We administered verbal memory (word recall and word recognition) and executive function tasks (word fluency test, forward and backward digit and visual span tests, Kana Pick-out Test, Trail Making Test, and conflicting instructions and a Go/NoGo task from the Frontal Assessment Battery). We found that patients with SCA3 had significantly lower scores than the healthy control subjects on the word recall, semantic, and letter fluency, and backward digit span tests, while word recognition was well preserved. The other executive function tests showed preserved functions in the SCA3 group, indicating that visual working memory, and attention and inhibition control were not affected. The patients with SCA3 showed impaired word recall and intact word recognition, and accordingly, episodic memory encoding and storage processes in short-term memory were preserved. In category and letter-fluency tests, impairment was attributable to word-retrieval from semantic memory. Impaired verbal working memory may be involved in the retrieval of verbal information from phonological storage by means of continuous subvocal rehearsal, rather than a deficit in initial phonological encoding. Essential executive dysfunction in patients with SCA3 may be due to damage in the cerebellar cortex-ventral dentate nucleus-thalamus-prefrontal cortex circuits, which are involved in strategic retrieval of verbal information from different modes of memory storage.

TVA-Based Assessment of Visual Attention Using Line-Drawings of Fruits and Vegetables.

Visuospatial attention and short-term memory allow us to prioritize, select, and briefly maintain part of the visual information that reaches our senses. These cognitive abilities are quantitatively accounted for by Bundesen’s theory of visual attention (TVA; Bundesen, 1990). Previous studies have suggested that TVA-based assessments are sensitive to inter-individual differences in spatial bias, visual short-term memory capacity, top-down control, and processing speed in healthy volunteers as well as in patients with various neurological and psychiatric conditions. However, most neuropsychological assessments of attention and executive functions, including TVA-based assessment, make use of alphanumeric stimuli and/or are performed verbally, which can pose difficulties for individuals who have troubles processing letters or numbers. Here we examined the reliability of TVA-based assessments when stimuli are used that are not alphanumeric, but instead based on line-drawings of fruits and vegetables. We compared five TVA parameters quantifying the aforementioned cognitive abilities, obtained by modeling accuracy data on a whole/partial report paradigm using conventional alphabet stimuli versus the food stimuli. Significant correlations were found for all TVA parameters, indicating a high parallel-form reliability. Split-half correlations assessing internal reliability, and correlations between predicted and observed data assessing goodness-of-fit were both significant. Our results provide an indication that line-drawings of fruits and vegetables can be used for a reliable assessment of attention and short-term memory.

History dependence in insect flight decisions during odor tracking.

Natural decision-making often involves extended decision sequences in response to variable stimuli with complex structure. As an example, many animals follow odor plumes to locate food sources or mates, but turbulence breaks up the advected odor signal into intermittent filaments and puffs. This scenario provides an opportunity to ask how animals use sparse, instantaneous, and stochastic signal encounters to generate goal-oriented behavioral sequences. Here we examined the trajectories of flying fruit flies (Drosophila melanogaster) and mosquitoes (Aedes aegypti) navigating in controlled plumes of attractive odorants. While it is known that mean odor-triggered flight responses are dominated by upwind turns, individual responses are highly variable. We asked whether deviations from mean responses depended on specific features of odor encounters, and found that odor-triggered turns were slightly but significantly modulated by two features of odor encounters. First, encounters with higher concentrations triggered stronger upwind turns. Second, encounters occurring later in a sequence triggered weaker upwind turns. To contextualize the latter history dependence theoretically, we examined trajectories simulated from three normative tracking strategies. We found that neither a purely reactive strategy nor a strategy in which the tracker learned the plume centerline over time captured the observed history dependence. In contrast, “infotaxis”, in which flight decisions maximized expected information gain about source location, exhibited a history dependence aligned in sign with the data, though much larger in magnitude. These findings suggest that while true plume tracking is dominated by a reactive odor response it might also involve a history-dependent modulation of responses consistent with the accumulation of information about a source over multi-encounter timescales. This suggests that short-term memory processes modulating decision sequences may play a role in natural plume tracking.

Dissociating Long and Short-term Memory in Three-Month-Old Infants Using the Mismatch Response to Voice Stimuli.

Auditory event-related potentials (ERPs) have been successfully used in adults as well as in newborns to discriminate recall of longer-term and shorter-term memories. Specifically the Mismatch Response (MMR) to deviant stimuli of an oddball paradigm is larger if the deviant stimuli are highly familiar (i.e., retrieved from long-term memory) than if they are unfamiliar, representing an immediate change to the standard stimuli kept in short-term memory. Here, we aimed to extend previous findings indicating a differential MMR to familiar and unfamiliar deviants in newborns (Beauchemin et al., 2011), to 3-month-old infants who are starting to interact more with their social surroundings supposedly based on forming more (social) long-term representations. Using a voice discrimination paradigm, each infant was repeatedly presented with the word “baby” (400 ms, interstimulus interval: 600 ms, 10 min overall duration) pronounced by three different female speakers. One voice that was unfamiliar to the infants served as the frequently presented “standard” stimulus, whereas another unfamiliar voice served as the “unfamiliar deviant” stimulus, and the voice of the infant’s mother served as the “familiar deviant.” Data collection was successful for 31 infants (mean age = 100 days). The MMR was determined by the difference between the ERP to standard stimuli and the ERP to the unfamiliar and familiar deviant, respectively. The MMR to the familiar deviant (mother’s voice) was larger, i.e., more positive, than that to the unfamiliar deviant between 100 and 400 ms post-stimulus over the frontal and central cortex. However, a genuine MMR differentiating, as a positive deflection, between ERPs to familiar deviants and standard stimuli was only found in the 300–400 ms interval. On the other hand, a genuine MMR differentiating, as a negative deflection, between ERPs to unfamiliar deviants from ERPs to standard stimuli was revealed for the 200–300 ms post-stimulus interval. Overall results confirm a differential MMR response to unfamiliar and familiar deviants in 3-month-olds, with the earlier negative MMR to unfamiliar deviants likely reflecting change detection based on comparison processes in short-term memory, and the later positive MMR to familiar deviants reflecting subsequent long-term memory-based processing of stimulus relevance.

Hubungan antara Status Mood dan Fungsi Kognitif dalam Kalangan Warga Emas yang Mempunyai Kecelaan Kognitif Ringan

There is some evidence stated that mood states might influence cognitive functioning, such as episodic memory, working memory and creative problem solving. This study was conducted to evaluate the relationship between mood states and cognitive functioning among older adults with Mild Cognitive Impairment (MCI). This study involved 12 male and 37 female subjects from Klang Valley aged 60 year old and above. MCI was defined based on criteria proposed by Peterson. Cognitive functions of the subjects were accessed using Mini Mental State Examination (MMSE), Rey Auditory Verbal Learning Test (RAVLT), Digit Span, Digit Symbol Substituition Test (DSST) and Visual Reproduction; while mood states including tension, depression, anger, vigour, esteem related affect, fatigue and confusion were accessed using Profile of Mood States (POMS) questionnaire. Total positive subscales score, total negative subscales score and total mood disturbance (TMD) were also calculated. There were significant positive correlations between tension (r = 0.325, p = 0.30), vigour (r = 0.235, p = 0.036), esteem related affect (r = 0.316, p = 0.034) and total positive subscales score (r = 0.307, p = 0.040) with verbal episodic memory as measured using RAVLT fifth trial. In addition, positive correlations were also observed between vigour (r = 0.228, p = 0.035) and total positive subscales score (r = 0.237, p = 0.025) with DSST. After adjusted for confounding factors, subjects who scored higher in esteem related affect (Adjusted OR = 0.390, 95% CI [0.069-0.711], p = 0.019) and tension (Adjusted OR = 0.253, 95% CI [0.075-0.431], p = 0.007) had better verbal episodic memory. Subjects who have higher total positive subscales score were also had faster processing speed (OR = 0.856, 95% CI [0.099-1.614], p = 0.028). However after adjusted for confounding factors, the relationship was not significant (Adjusted OR = 0.383, 95% CI [-0.247-1.013], p = 2.226). Older adults with MCI who had a more positive mood tend to have a better short-term verbal memory and faster processing speed. DOI : http://dx.doi.org./10.17576/JSKM-2018-42

Hubungan antara Status Mood dan Fungsi Kognitif dalam Kalangan Warga Emas yang Mempunyai Kecelaan Kognitif Ringan

There is some evidence stated that mood states might influence cognitive functioning, such as episodic memory, working memory and creative problem solving. This study was conducted to evaluate the relationship between mood states and cognitive functioning among older adults with Mild Cognitive Impairment (MCI). This study involved 12 male and 37 female subjects from Klang Valley aged 60 year old and above. MCI was defined based on criteria proposed by Peterson. Cognitive functions of the subjects were accessed using Mini Mental State Examination (MMSE), Rey Auditory Verbal Learning Test (RAVLT), Digit Span, Digit Symbol Substituition Test (DSST) and Visual Reproduction; while mood states including tension, depression, anger, vigour, esteem related affect, fatigue and confusion were accessed using Profile of Mood States (POMS) questionnaire. Total positive subscales score, total negative subscales score and total mood disturbance (TMD) were also calculated. There were significant positive correlations between tension (r = 0.325, p = 0.30), vigour (r = 0.235, p = 0.036), esteem related affect (r = 0.316, p = 0.034) and total positive subscales score (r = 0.307, p = 0.040) with verbal episodic memory as measured using RAVLT fifth trial. In addition, positive correlations were also observed between vigour (r = 0.228, p = 0.035) and total positive subscales score (r = 0.237, p = 0.025) with DSST. After adjusted for confounding factors, subjects who scored higher in esteem related affect (Adjusted OR = 0.390, 95% CI [0.069-0.711], p = 0.019) and tension (Adjusted OR = 0.253, 95% CI [0.075-0.431], p = 0.007) had better verbal episodic memory. Subjects who have higher total positive subscales score were also had faster processing speed (OR = 0.856, 95% CI [0.099-1.614], p = 0.028). However after adjusted for confounding factors, the relationship was not significant (Adjusted OR = 0.383, 95% CI [-0.247-1.013], p = 2.226). Older adults with MCI who had a more positive mood tend to have a better short-term verbal memory and faster processing speed. DOI : http://dx.doi.org./10.17576/JSKM-2018-42

Temporal grouping effects in musical short-term memory

ABSTRACTRecent theoretical accounts of verbal and visuo-spatial short-term memory (STM) have proposed the existence of domain-general mechanisms for the maintenance of serial order information. These accounts are based on the observation of similar behavioural effects across several modalities, such as temporal grouping effects. Across two experiments, the present study aimed at extending these findings, by exploring a STM modality that has received little interest so far, STM for musical information. Given its inherent rhythmic, temporal and serial organisation, the musical domain is of interest for investigating serial order STM processes such as temporal grouping. In Experiment 1, the data did not allow to determine the presence or the absence of temporal grouping effects. In Experiment 2, we observed that temporal grouping of tone sequences during encoding improves short-term recognition for serially presented probe tones. Furthermore, the serial position curves included micro-primacy and micro-recency effects, which are the hallmark characteristic of temporal grouping. Our results suggest that the encoding of serial order information in musical STM may be supported by temporal positional coding mechanisms similar to those reported in the verbal domain.

Verbal short-term memory shows a specific association with receptive but not productive vocabulary measures in Down syndrome.

Verbal short-term memory (STM) capacity has been considered to support vocabulary learning in typical children and adults, but evidence for this link is inconsistent for studies in individuals with Down syndrome (DS). The aim of this study was explore the role of processing demands on the association between verbal STM and vocabulary measures in DS, by comparing receptive vocabulary measures with high STM processing demands to productive vocabulary measures with low STM processing demands. Forty-seven adults with Down syndrome were administered receptive vocabulary and productive vocabulary tasks, as well as measures of verbal STM abilities and intellectual efficiency. Bayesian regression analyses showed that verbal STM abilities were strongly and specifically associated with receptive vocabulary measures but not productive lexical abilities after controlling for intellectual efficiency, and this is despite the fact that vocabulary abilities as measured by receptive and productive vocabulary tasks were closely associated. In Down syndrome, verbal STM abilities may be predictive of specific task demands associated with receptive vocabulary tasks rather than of vocabulary development per se.

Dynamics of high frequency brain activity

Evidence suggests that electroencephalographic (EEG) activity extends far beyond the traditional frequency range. Much of the prior study of >120 Hz EEG is in epileptic brains. In the current work, we measured EEG activity in the range of 200 to 2000 Hz, in the brains of healthy, spontaneously behaving rats. Both arrhythmic (1/f-type) and rhythmic (band) activities were identified and their properties shown to depend on EEG-defined stage of sleep/wakefulness. The inverse power law exponent of 1/f-type noise is shown to decrease from 3.08 in REM and 2.58 in NonREM to a value of 1.99 in the Waking state. Such a trend represents a transition from long- to short-term memory processes when examined in terms of the corresponding Hurst index. In addition, treating the 1/f-type activity as baseline noise reveals the presence of two, newly identified, high frequency EEG bands. The first band (ψ) is centered between 260–280 Hz; the second, and stronger, band is a broad peak in the 400–500 Hz range (termed ω). Both of these peaks display lognormal distributions. The functional significance of these frequency bands is supported by the variation in the strength of the peaks with EEG-defined sleep/wakefulness.

Letter and symbol identification: No evidence for letter-specific crowding mechanisms.

It has been proposed that letters, as opposed to symbols, trigger specialized crowding processes, boosting identification of the first and last letters of words. This hypothesis is based on evidence that single-letter accuracy as a function of within-string position has a W shape (the classic serial position function [SPF] in psycholinguistics) whereas an inverted V shape is obtained when measured with symbols. Our main goal was to test the robustness of the latter result. Our hypothesis was that any letter/symbol difference might result from short-term visual memory processes (due to the partial report [PR] procedures used in SPF studies) rather than from crowding. We therefore removed the involvement of short-term memory by precueing target-item position and compared SPFs with precueing and postcueing. Perimetric complexity was stringently matched between letters and symbols. In postcueing conditions similar to previous studies, we did not reproduce the inverted V shape for symbols: Clear-cut W shapes were observed with an overall smaller accuracy for symbols compared to letters. This letter/symbol difference was dramatically reduced in precueing conditions in keeping with our prediction. Our results are not consistent with the claim that letter strings trigger specialized crowding processes. We argue that PR procedures are not fit to isolate crowding processes.

Learning written word vocabulary in a second language: Theoretical and practical implications

Short-term memory (STM) is required for second language learning. However, it is not clear what components of STM are necessary for the acquisition and lexicalisation of new written words. Studies suggest that memory for serial order is a critical cognitive process in spoken word acquisition although correlated mechanisms such as executive control also play a role. In this study, bilingual Cantonese–English speakers who are learning written expert words in a non-native language were tested over a one year period in their first year of instruction. Written word lexicalisation was measured using lexical decision and spelling to dictation tasks. Results showed measures of executive control (Stroop performance) and serial order memory capacity predict recognition and recall of written expert words at different stages. Whereas serial order memory predicts improvements to lexical decision accuracy, executive control predicts spelling to dictation performance after one year. The conclusion is that STM processes do constrain written word lexicalisation in a second language. However, executive control and serial order memory capacity have differential effects during word lexicalisation.

The Difference of CD4 Count Between HIV Positive Patients With Cognitive Decline and Without Cognitive Decline

The relationship between low absolute CD4 lymphocyte count and neurological complications is well established in the era preceding highly active antiretroviral therapy (HAART). The aims of this study to assess the proportion of cognitive decline among HIV outclinic patient Sardjito General Hospital Yogyakarta and to determine whether the difference of CD4 count between HIV positive patients with cognitive decline and without cognitive decline. A cross sectional study with consecutive sampling. Subject eligible were 15-50 years of age, without a history of stroke, brain injury, CNS tumor and Parkinson’s disease wich devided into 2 groups (CD4 > 200 cel/mm3 and d”200 cel/mm3). Cognitive function was measured by using MMSE and specified for each domain. Digit span and Trail Making Test B were added to further analyze short term memory and motor processing speed and they perform CD4 count in their blood. Ninety six patients fulfill inclution and exclution criteria. Proportion of cognitive decline was 33.3% among HIV patient. Univariate analysis showed significant difference of CD4 count between HIV positive patients with cognitive decline and without cognitive decline (p=0.02). CD4 count was significantly different in the decline of all cognitive domain on MMSE, also in the decline of short term memory and processing speed. There are high of cognitive decline among HIV outclinic patient Sardjito General Hospital Yogyakarta. CD4 count are difference between HIV positive patients with cognitive decline and without cognitive decline.

Differences of temporal dynamics and signal complexity of gamma band oscillations in first-episode psychosis during a working memory task.

Gamma band oscillations participate in the temporal binding needed to synchronize cortical networks, involved in early sensory and short term memory processes. In earlier studies, alterations of these neurophysiological parameters have been found in psychotic disorders. To date no study has explored the temporal dynamics and signal complexity of gamma band oscillations in first episode psychosis (FEP). To address this issue, gamma band analysis was performed in 15 FEP patients and 18 healthy controls who successfully performed an adapted 2-back working memory task. Multiple linear and logistic regression models were computed to explore the relationship between the cognitive status and gamma oscillation changes over time. Based on regression model results, phase diagrams were constructed and their complexity was estimated using fractal dimension, a mathematical tool that describes shapes as numeric values. When adjusted for gamma values at time lags -3 to -4ms and -15 to -16ms, FEP patients displayed significantly higher time-dependent changes than controls, independently of the nature of the task. The present results are consistent with a discoordination of the activity of cortical generators engaged by the stimulus apparition in FEP patients, leading to a global binding deficit. In addition, fractal analysis showing higher complexity of gamma signal, confirmed this deficit. Our results provide evidence for recruitment of supplementary cortical generators as compensating mechanisms and yield further understanding for the pathophysiology cognitive impairments in FEP.

Some Neurocognitive Correlates of Noise-Vocoded Speech Perception in Children With Normal Hearing: A Replication and Extension of ).

Noise-vocoded speech is a valuable research tool for testing experimental hypotheses about the effects of spectral degradation on speech recognition in adults with normal hearing (NH). However, very little research has utilized noise-vocoded speech with children with NH. Earlier studies with children with NH focused primarily on the amount of spectral information needed for speech recognition without assessing the contribution of neurocognitive processes to speech perception and spoken word recognition. In this study, we first replicated the seminal findings reported by ) who investigated effects of lexical density and word frequency on noise-vocoded speech perception in a small group of children with NH. We then extended the research to investigate relations between noise-vocoded speech recognition abilities and five neurocognitive measures: auditory attention (AA) and response set, talker discrimination, and verbal and nonverbal short-term working memory. Thirty-one children with NH between 5 and 13 years of age were assessed on their ability to perceive lexically controlled words in isolation and in sentences that were noise-vocoded to four spectral channels. Children were also administered vocabulary assessments (Peabody Picture Vocabulary test-4th Edition and Expressive Vocabulary test-2nd Edition) and measures of AA (NEPSY AA and response set and a talker discrimination task) and short-term memory (visual digit and symbol spans). Consistent with the findings reported in the original ) study, we found that children perceived noise-vocoded lexically easy words better than lexically hard words. Words in sentences were also recognized better than the same words presented in isolation. No significant correlations were observed between noise-vocoded speech recognition scores and the Peabody Picture Vocabulary test-4th Edition using language quotients to control for age effects. However, children who scored higher on the Expressive Vocabulary test-2nd Edition recognized lexically easy words better than lexically hard words in sentences. Older children perceived noise-vocoded speech better than younger children. Finally, we found that measures of AA and short-term memory capacity were significantly correlated with a child's ability to perceive noise-vocoded isolated words and sentences. First, we successfully replicated the major findings from the ) study. Because familiarity, phonological distinctiveness and lexical competition affect word recognition, these findings provide additional support for the proposal that several foundational elementary neurocognitive processes underlie the perception of spectrally degraded speech. Second, we found strong and significant correlations between performance on neurocognitive measures and children's ability to recognize words and sentences noise-vocoded to four spectral channels. These findings extend earlier research suggesting that perception of spectrally degraded speech reflects early peripheral auditory processes, as well as additional contributions of executive function, specifically, selective attention and short-term memory processes in spoken word recognition. The present findings suggest that AA and short-term memory support robust spoken word recognition in children with NH even under compromised and challenging listening conditions. These results are relevant to research carried out with listeners who have hearing loss, because they are routinely required to encode, process, and understand spectrally degraded acoustic signals.