Task-related Differences Research Articles

Influence of Task Combination on EEG Spectrum Modulation for Driver Workload Estimation

This study investigates the feasibility of using a method based on electroencephalography (EEG) for deriving a driver's mental workload index. The psychophysiological signals provide sensitive information for human functional states assessment in both laboratory and real-world settings and for building a new communication channel between driver and vehicle that allows for driver workload monitoring. An experiment combining a lane-change task and n-back task was conducted. The task load levels were manipulated in two dimensions, driving task load and working memory load, with each containing three task load conditions. The frontal theta activity showed significant increases in the working memory load dimension, but differences were not found with the driving task load dimension. However, significant decreases in parietal alpha activity were found when the task load was increased in both dimensions. Task-related differences were also found. The driving task load contributed more to the changes in alpha power, whereas the working memory load contributed more to the changes in theta power. Additionally, these two task load dimensions caused significant interactive effects on both theta and alpha power. These results indicate that EEG technology can provide sensitive information for driver workload detection even if the sensitivities of different EEG parameters tend to be task dependent. One potential future application of this study is to establish a general driver workload estimator that uses EEG signals.

Impaired response inhibition in ill Gulf War veterans

Poor performance on tasks requiring response inhibition has been observed among chronically ill veterans of the 1991 Persian Gulf War. Semantic difficulties have also been reported. We collected event-related potential (ERP) and behavioral data from 25 Gulf War veterans who complained of cognitive difficulties and from 23 matched controls, who were deployed but not symptomatic, while they performed a GO–NOGO task that required both a semantic decision and inhibitory processing. A significantly greater false-alarm rate among the ill veterans was accompanied in the ERP data by significantly reduced amplitude in the NOGO P3, consistent with previous ERP studies of other patient groups that have shown poor inhibitory response performance. This supports the contention that the ill veterans' deficit lies more in inhibiting than in detecting task-related differences in the stimuli.

Task-related differences in temporo-parietal cortical activation during human phonatory behaviors

Functional magnetic resonance imaging (fMRI) was used to investigate cortical activity related to differential control of the human phonatory system during a sentence production task. Our focus in this report was on activation of the temporo-parietal (TP) junctional region, suggested by recent models in speech production/perception to play a critical role between self-generated acoustic and associated somatosensory inputs related to the consequences of speech. Thirteen healthy participants produced multiple trials of phonetically balanced sentences during each of three performance conditions: “covert”, “whisper” and “voice”. An event-related, sparse sampling fMRI method was used to examine TP activity associated with sentence production during each condition. Results demonstrated differential responsiveness in the TP region bilaterally as a function of task conditions, with covert production generating the highest level of TP activation. These results suggest that the TP region is differentially responsive to phonation-specific production variables. Our finding that covert production instead of overt voicing resulted in the greatest activity in TP is consistent with recent reports demonstrating TP activation related to temporal ordering judgments and task-dependent memory use.

The cuticular hydrocarbons profiles in the stingless bee Melipona marginata reflect task-related differences

Members of social insect colonies employ a large variety of chemical signals during their life. Of these, cuticular hydrocarbons are of primary importance for social insects since they allow for the recognition of conspecifics, nestmates and even members of different castes. The objectives of this study were (1) to characterize the variation of the chemical profiles among workers of the stingless bee Melipona marginata, and (2) to investigate the dependence of the chemical profiles on the age and on the behavior of the studied individuals. The results showed that cuticular hydrocarbon profiles of workers were composed of alkanes, alkenes and alkadienes that varied quantitatively and qualitatively according to function of workers in the colony.

Investigating the use of coherence analysis on mandibular electromyograms to investigate neural control of early oromandibular behaviours: A pilot study

An empirical method for investigating differences in neural control of jaw movement across oromandibular behaviours is to compute the coherence function for electromyographic signals obtained from mandibular muscle groups. This procedure has been used with adults but not extended to children. This pilot study investigated if coherence analysis could reveal task-related differences in control for children by measuring mandibular electromyograms obtained from an infant and adult. Electromyographic signals were obtained from bilateral masseter and temporalis muscle groups during chewing and babble from a typically developing infant from 8–22 months, and chewing and speech were obtained from an adult. Coherence functions were computed. Measures obtained from the infant and adult exhibited a significant main effect for task, with peak coherence values within 20–60 Hz being significantly greater for chewing than vocalization. This pilot study suggests that coherence analysis of mandibular EMG is a sensitive measure for distinguishing task-related differences in neural organization for children.

ERPs to infrequent auditory stimuli in two- and three-stimulus versions of the inter-modal oddball task

Previous research has shown that auditory targets in inter-modal oddball conditions are processed in two stages, an early modality-specific and a later context-dependent stage. The aim of this study was to investigate how the processing of auditory target stimuli is affected by the inclusion of an additional infrequent auditory non-target stimulus in inter-modal oddball conditions. 17 subjects received 300 stimuli in each of a two- and a three-stimulus version of the inter-modal oddball task. Both tasks included 240 (80%) presentations of a counter-phasing checkerboard randomly interspersed with 60 presentations of an auditory stimulus. In the two-stimulus condition subjects received 60 (20%) target stimuli. In the three-stimulus condition subjects received 30 (10%) target and 30 (10%) non-target stimuli. ERPs to the two target stimuli and ERPs to targets and auditory non-targets in the three-stimulus condition were investigated. Early components N100 and P200 were larger to non-targets than targets. N140, an additional frontal negativity in inter-modal oddball conditions, was larger in the three-stimulus compared with the two-stimulus condition. Targets produced two late positive components (P250/P3a and P300). In the three-stimulus task the P250/P3a was enhanced frontally and P300 was enhanced in right parietal regions. Non-target auditory stimuli produced a broad negativity (N285) at this latency. All stimuli produced a late positivity (P350) that demonstrated task-related topographic differences. The results are interpreted with respect to previous inter-modal oddball findings and research into auditory processing.

A comparison of brain activity evoked by single content and function words: An fMRI investigation of implicit word processing

Content and function words have different roles in language and differ greatly in their semantic content. Although previous research has suggested that these different roles may be mediated by different neural substrates, the neuroimaging literature on this topic is particularly scant. Moreover, fMRI studies that have investigated differences between content and function words have utilized tasks that focus the subjects' attention on the differences between these word types. It is possible, then, that task-related differences in attention, working memory, and decision-making contribute to the differential patterns of activation observed. Here, subjects were engaged in a continuous working memory cover task while single, task-irrelevant content and function words were infrequently and irregularly presented. Nonword letter strings were displayed in black font at a fast rate (2/s). Subjects were required to either remember or retrieve occasional nonwords that were presented in colored fonts. Incidental and irrelevant to the memory task, content and function words were interspersed among nonwords at intervals of 12 to 15 s. Both word types strongly activated temporal–parietal cortex, middle and anterior temporal cortex, inferior frontal gyrus, parahippocampal gyrus, and orbital frontal cortex. Activations were more extensive in the left hemisphere. Content words elicited greater activation than function words in middle and anterior temporal cortex, a sub-region of orbital frontal cortex, and the parahippocampal region. Words also evoked extensive deactivation, most notably in brain regions previously associated with working memory and attention.

Respiratory and Laryngeal Function During Spontaneous Speaking in Teachers With Voice Disorders

To determine if respiratory and laryngeal function during spontaneous speaking were different for teachers with voice disorders compared with teachers without voice problems. Eighteen teachers, 9 with and 9 without voice disorders, were included in this study. Respiratory function was measured with magnetometry, and laryngeal function was measured with electroglottography during 3 spontaneous speaking tasks: a simulated teaching task at a typical loudness level, a simulated teaching task at an increased loudness level, and a conversational speaking task. Electroglottography measures were also obtained for 3 structured speaking tasks: a paragraph reading task, a sustained vowel, and a maximum phonation time vowel. Teachers with voice disorders started and ended their breath groups at significantly smaller lung volumes than teachers without voice problems during teaching-related speaking tasks; however, there were no between-group differences in laryngeal measures. Task-related differences were found on several respiratory measures and on one laryngeal measure. These findings suggest that teachers with voice disorders used different speech breathing strategies than teachers without voice problems. Implications for clinical management of teachers with voice disorders are discussed.

A Developmental fMRI Study of Reading and Repetition Reveals Changes in Phonological and Visual Mechanisms Over Age

In this study of reading development, children (ages 7-10) and adults (ages 18-32) performed overt single-word reading and aural repetition tasks on high-frequency word stimuli during functional magnetic resonance imaging. Most regions showed similar activity across age groups. These widespread regions of similarity indicate that children and adults use largely overlapping mechanisms when processing high-frequency words. Significant task-related differences included greater activity in occipital cortex for the read task, and greater activity in temporal cortex for the repeat task; activity levels in these regions were similar for adults and children. However, age group differences were found in several posterior regions, including a set of regions implicated in adult reading: the left supramarginal gyrus, the left angular gyrus, and bilateral anterior extrastriate cortex. The angular and supramarginal gyrus regions, hypothesized to play a role in phonology, showed decreased activity in adults relative to children for high-frequency words. The extrastriate regions had significant activity for both the visual read task and auditory repeat task in children, but just for the read task in adults, showing significant task and age interactions. These results are consistent with decreasing reliance on phonological processing, and increasing tuning of visual mechanisms, with age.

The Role of Expectancies in Accepting Task-Related Diversity: Do Disappointment and Lack of Commitment Stem From Actual Differences or Violated Expectations?

Two studies show that initial expectancies influence the way people respond toward task-related differences (i.e., in work goals or work styles) between the self and a collaboration partner. When no advance information is available, participants expect their partner to be similar to themselves in task-related aspects. However, when people expect their partner to have a different work goal (Study 1) or work style (Study 2), and this actually is the case, disappointment is reduced and commitment toward future collaboration is increased. Initial expectations are important because these help people develop a clear picture of their partner. When initial expectations are violated, people conceive the other less clearly and this is part of the reason they report lower levels of commitment.

Top-Down Control-Signal Dynamics in Anterior Cingulate and Prefrontal Cortex Neurons following Task Switching

The prefrontal cortex (PFC) and anterior cingulate cortex (ACC) have both been implicated in cognitive control, but their relative roles remain unclear. Here we recorded the activity of single neurons in both areas while monkeys performed a task that required them to switch between trials in which they had to look toward a flashed stimulus (prosaccades) and trials in which they had to look away from the stimulus (antisaccades). We found that ACC neurons had a higher level of task selectivity than PFC neurons during the preparatory period on trials immediately following a task switch. In ACC neurons, task selectivity was strongest after the task switch and declined throughout the task block, whereas task selectivity remained constant in the PFC. These results demonstrate that the ACC is recruited when cognitive demands increase and suggest a role for both areas in task maintenance and the implementation of top-down control.

Different temporal profiles of amnesia after intra-hippocampus and intra-amygdala infusions of anisomycin.

Systemic or intra-hippocampal administration of the protein synthesis inhibitor anisomycin generally leads to impairments in memory tested 24 hr or more after training but spares memory for a few hours after training. Thus, amnesia does not appear immediately after training but develops with time, findings most often interpreted as evidence for distinct short- and long-term memory processes. However, time courses for the onset of amnesia vary substantially after treatment with protein synthesis inhibitors. Some of the variability across experiments may reflect task-related differences or, perhaps relatedly, may reflect memory processing mediated by different neural systems. In the present experiments, anisomycin was infused into either the hippocampus or the amygdala 20 min before inhibitory avoidance training. Similar to previous findings, intra-hippocampus injections of anisomycin impaired memory tested 48 hr after training yet spared memory tested 4 hr after training. In contrast, intra-amygdala injections of anisomycin impaired memory tested at 0.5, 4, and 48 hr after training, revealing no evidence for spared memory at short times after training. The distinct temporal properties for amnesia following anisomycin injections into the hippocampus or amygdala may reflect different consequences for memory of perturbations of the neural system in which the manipulation is made.

Enhancement of Object Representations in Primate Perirhinal Cortex During a Visual Working-Memory Task

We compared single-cell activities in perirhinal cortex (PRh) as well as adjacent visual cortex (area TE) across two tasks. One task required the monkey to identify any stimulus repetition within a sequence of object stimuli. In the other task, the same stimuli were presented, but the monkey didn't have to remember them. PRh responses during the object-memory task were elevated relative to those during the second task. In TE, on the other hand, there were no significant task-related differences in responses. We did not observe task-related differences related to repetition effects in either brain area. The onset of the enhanced signal in PRh during the object-memory task occurred with a latency of 80 ms after the onset of the stimulus response, suggesting that it was the result of top-down feedback.

Morpho-syntactic and morpho-phonological deficits in the production of regularly and irregularly inflected verbs

Background: The background to the study is the debate in relation to the English regular/irregular past tense forms.Aims: The purpose of the investigation was the evaluation of the dual mechanism (DMT: Pinker, 1999; Marslen-Wilson & Tyler, 1997, 1998; Ullman, Corkin, Coppola, Hickok, Growdon, Koroshetz, et al., 1997) and connectionist single mechanism models (SMT: Bird, Lambon Ralph, Seidenberg, McClelland, & Patterson, 2003; Joanisse & Seidenberg, 1999; Patterson, Lambon Ralph, Hodges, & McClelland, 2001) through exploring the reading and oral production of regular and irregular past tense forms and other verbal and nominal inflections by a Broca's type aphasic and phonological dyslexic patient.Methods & Procedures: Eight experimental tasks are reported. Three involved the reading of stems and inflected verbs and nouns in differently organised lists, two involved the oral production of past tense verbs and plural nouns, and three explored the ability to distinguish between written verbs inflected with various affixes.Outcomes & Results: In reading randomly organised list of nouns, verb stems, and regular and irregular past tense forms the patient displayed dissociation between regular and irregular past tense forms as predicted by DMT. When the same items were presented in a list with present and past tense forms paired, and in the oral transformation task, the dissociation disappeared, and performance in regular and irregular past tense forms became comparable. There was a difference in the patient's reading of plural nouns and progressive verbs, which was good, and of past tense forms and third person forms, which was impaired. The recognition/comprehension tasks revealed that the patient was aware of the presence of an affix, but he could not reliably distinguish between different affixes.Conclusions: Performance on regular/irregular past tense forms and the variable levels of performance in producing different regular inflections are in conflict with both DMT and SMT on a number of grounds. The task-related differences between randomly organised lists and paired present and past tense forms are accounted for by distinguishing between morpho-phonological and morpho-syntactic effects. It is argued that deficits confined to the production of regular past tense forms are morpho-phonological in nature, while deficits in both regular and irregular past tense forms originate in morpho-syntax. Since SMT and DMT are theories of morpho-phonological processes, they cannot account for the complex performance pattern presented by the patient in the present study and by other similar patients. The differences attested in the availability of differently affixed words and deficits in irregular past tense forms are only accountable at the level of morpho-syntax.

“What” versus “Where” in the audiovisual domain: An fMRI study

Similar “what/where” functional segregations have been proposed for both visual and auditory cortical processing. In this fMRI study, we investigated if the same segregation exists in the crossmodal domain, when visual and auditory stimuli have to be matched in order to perform either a recognition or a localization task. Recent neuroimaging research highlighted the contribution of different heteromodal cortical regions during various forms of crossmodal binding. Interestingly, crossmodal effects during audiovisual speech and object recognition have been found in the superior temporal sulcus, while crossmodal effects during the execution of spatial tasks have been found over the intraparietal sulcus, suggesting an underlying “what/where” segregation. In order to directly compare the specific involvement of these two heteromodal regions, we scanned ten male right-handed subjects during the execution of two crossmodal matching tasks. Participants were simultaneously presented with a picture and an environmental sound, coming from either the same or the opposite hemifield and representing either the same or a different object. The two tasks required a manual YES/NO response respectively about location or semantic matching of the presented stimuli. Both group and individual subject analysis were performed. Task-related differences in BOLD response were observed in the right intraparietal sulcus and in the left superior temporal sulcus, providing a direct confirmation of the “what–where” functional segregation in the crossmodal audiovisual domain.

Age and task-related differences in timing stability, consistency, and natural frequency of children's rhythmic, motor coordination

How does task complexity affect performance in a rhythmic movement task across childhood and into adulthood? The purpose of this experiment was to compare the frequency, stability, and consistency of clapping and walking when these tasks were produced individually and simultaneously by children of different ages. Statistically significant differences were found in natural frequency, stability, and consistency between tasks, limb actions, and among age groups. The results indicated that action-dependent, age-related differences existed. Further, task-related differences existed in these measures that were constant across age groups. This suggested that the role of task was as important as changing morphologies in determining action characteristics across childhood.

Discrimination and categorization of speech and non-speech sounds in an MEG delayed-match-to-sample study

We investigated the perception and categorization of speech (vowels, syllables) and non-speech (tones, tonal contours) stimuli using MEG. In a delayed-match-to-sample paradigm, participants listened to two sounds and decided if they sounded exactly the same or different (auditory discrimination, AUD), or if they belonged to the same or different categories (category discrimination, CAT). Stimuli across the two conditions were identical; the category definitions for each kind of sound were learned in a training session before recording. MEG data were analyzed using an induced wavelet transform method to investigate task-related differences in time–frequency patterns. In auditory cortex, for both AUD and CAT conditions, an alpha (8–13 Hz) band activation enhancement during the delay period was found for all stimulus types. A clear difference between AUD and CAT conditions was observed for the non-speech stimuli in auditory areas and for both speech and non-speech stimuli in frontal areas. The results suggest that alpha band activation in auditory areas is related to both working memory and categorization for new non-speech stimuli. The fact that the dissociation between speech and non-speech occurred in auditory areas, but not frontal areas, points to different categorization mechanisms and networks for newly learned (non-speech) and natural (speech) categories.

Gamma Abnormalities During Perception of Illusory Figures in Autism

This experiment was designed to test the hypothesis that perceptual abnormalities in autism might be associated with alteration of induced gamma activity patterns overlying visual cortical regions. EEG was recorded from six adolescents with autism and eight controls matched on chronological age, and verbal and nonverbal mental age, whilst identifying the presence or absence of an illusory Kanizsa shape. Although there were no reaction time or accuracy differences between the groups there were significant task-related differences in cortical activity. Control participants showed typical gamma- band activity over parietal regions at around 350 msec post onset of shape trials, similar to gamma patterns found in previous studies with non-impaired adults. In contrast, autistic participants showed overall increased activity, including an early 100 msec gamma peak and a late induced peak, 50 to 70 msec earlier than that shown by the control group. We interpret the abnormal gamma activity to reflect decreased “signal to noise” due to decreased inhibitory processing. In this experiment we did not establish a link between altered perception and abnormal gamma, as the autistic participants' behaviour did not differ from the controls. Future work should be designed to replicate this phenomenon and establish the perceptual consequences of altered gamma activity.

Variations in articulatory movement with changes in speech task.

Studies of normal and disordered articulatory movement often rely on the use of short, simple speech tasks. However, the severity of speech disorders can be observed to vary markedly with task. Understanding task-related variations in articulatory kinematic behavior may allow for an improved understanding of normal and disordered speech motor behavior in varying communication contexts. This study evaluated how orofacial kinematic behavior varies as a function of speaking task in a group of 15 healthy male speakers. The speech tasks included a nonsense phrase with a high frequency of stop consonants, a sentence, an oral reading passage, and a spontaneous monologue. In addition, rate and intensity conditions were varied for the nonsense phrase and sentence. The articulatory positions of the upper lip, lower lip, tongue blade, and mandible were recorded, and measures reflecting (a). average features of individual movements or strokes (i.e., peak speed, distance, and duration) and (b). overall spatial variability of the articulators for each task were extracted, derived, and analyzed. Results showed a number of task- and condition-related differences in speech kinematic behavior. The most prominent result from the task comparison was that the nonsense speech task exhibited larger, faster, and longer movement strokes than the other speech tasks. For some articulators (lower lip and tongue), there were task-related differences in spatial variability. Changes in loudness and rate revealed variation in kinematic measures that were often complicated by articulator identity and task type. The results suggest that an expanded range of speech tasks and conditions may aid in the study of normal and disordered speech motor behavior.

Effects of noise from functional magnetic resonance imaging on auditory event-related potentials in working memory task

The effects of functional magnetic resonance imaging (fMRI) acoustic noise were investigated on the parameters of event-related responses (ERPs) elicited during auditory matching-to-sample location and pitch working memory tasks. Stimuli were tones with varying location (left or right) and frequency (high or low). Subjects were instructed to memorize and compare either the locations or frequencies of the stimuli with each other. Tape-recorded fMRI acoustic noise was presented in half of the experimental blocks. The fMRI noise considerably enhanced the P1 component, reduced the amplitude and increased the latency of the N1, shortened the latency of the N2, and enhanced the amplitude of the P3 in both tasks. The N1 amplitude was higher in the location than pitch task in both noise and no-noise blocks, whereas the task-related N1 latency difference was present in the no-noise blocks only. Although the task-related differences between spatial and nonspatial auditory responses were partially preserved in noise, the finding that the acoustic gradient noise accompanying functional MR imaging modulated the auditory ERPs implies that the noise may confound the results of auditory fMRI experiments especially when studying higher cognitive processing.