Fnirs Research Papers - Academia.edu (original) (raw)

Recent advances in neuroimaging demonstrate the potential of functional near-infrared spectroscopy (fNIRS) for use in brain–computer interfaces (BCIs). fNIRS uses light in the near-infrared range to measure brain surface haemoglobin... more

Recent advances in neuroimaging demonstrate the potential of functional near-infrared spectroscopy (fNIRS) for use in brain–computer interfaces (BCIs). fNIRS uses light in the near-infrared range to measure brain surface haemoglobin concentrations and thus determine human neural activity. Our primary goal in this study is to analyse brain haemodynamic responses for application in a BCI. Specifically, we develop an efficient signal processing algorithm to extract important mental-task-relevant neural features and ...

A brain-computer interface (BCI) is a communication system that allows the use of brain activity to control computers or other external devices. It can, by bypassing the peripheral nervous system, provide a means of communication for... more

A brain-computer interface (BCI) is a communication system that allows the use of brain activity to control computers or other external devices. It can, by bypassing the peripheral nervous system, provide a means of communication for people suffering from severe motor disabilities or in a persistent vegetative state. In this paper, brain-signal generation tasks, noise removal methods, feature extraction/selection schemes, and classification techniques for fNIRS-based BCI are reviewed. The most common brain areas for fNIRS BCI are the primary motor cortex and the prefrontal cortex. In relation to the motor cortex, motor imagery tasks were preferred to motor execution tasks since possible proprioceptive feedback could be avoided. In relation to the prefrontal cortex, fNIRS showed a significant advantage due to no hair in detecting the cognitive tasks like mental arithmetic, music imagery, emotion induction, etc. In removing physiological noise in fNIRS data, band-pass filtering was mostly used. However, more advanced techniques like adaptive filtering, independent component analysis, multi optodes arrangement, etc. are being pursued to overcome the problem that a band-pass filter cannot be used when both brain and physiological signals occur within a close band. In extracting features related to the desired brain signal, the mean, variance, peak value, slope, skewness, and kurtosis of the noised-removed hemodynamic response were used. For classification, the linear discriminant analysis method provided simple but good performance among others: support vector machine, hidden Markov model, artificial neural network, etc. fNIRS will be more widely used to monitor the occurrence of neuro-plasticity after neuro-rehabilitation and neuro-stimulation. Technical breakthroughs in the future are expected via bundled-type probes, hybrid EEG-fNIRS BCI, and through the detection of initial dips.

After 800,000 years of making simple Oldowan tools, early humans began manufacturing Acheulian handaxes around 1.75 million years ago. This advance is hypothesized to reflect an evolutionary change in hominin cognition and language... more

After 800,000 years of making simple Oldowan tools, early humans began manufacturing Acheulian handaxes around 1.75 million years ago. This advance is hypothesized to reflect an evolutionary change in hominin cognition and language abilities. We used a neuroarchaeology approach to investigate this hypothesis, recording brain activity using functional near-infrared spectroscopy as modern human participants learned to make Oldowan and Acheulian stone tools in either a verbal or nonverbal training context. Here we show that Acheulian tool production requires the integration of visual, auditory and sensorimotor information in the middle and superior temporal cortex, the guidance of visual working memory representations in the ventral precentral gyrus, and higher-order action planning via the supplementary motor area, activating a brain network that is also involved in modern piano playing. The right analogue to Broca’s area—which has linked tool manufacture and language in prior work1,2—was only engaged during verbal training. Acheulian toolmaking, therefore, may have more evolutionary ties to playing Mozart than quoting Shakespeare.

Activity in medial prefrontal cortex (mPFC) during persuasive messages predicts future message-consistent behavior change, but there are significant limitations to the types of persuasion processes that can be invoked inside an MRI... more

Activity in medial prefrontal cortex (mPFC) during persuasive messages predicts future message-consistent behavior change, but there are significant limitations to the types of persuasion processes that can be invoked inside an MRI scanner. For instance, real world persuasion often involves multiple people in conversation. Functional near infrared spectroscopy (fNIRS) allows us to move out of the scanner and into more ecologically valid contexts. As a first step, the current study used fNIRS to replicate an existing fMRI persuasion paradigm (i.e. the sunscreen paradigm) to determine if mPFC shows similar predictive value with this technology. Consistent with prior fMRI work, activity in mPFC was significantly associated with message-consistent behavior change, above and beyond self-reported intentions. There was also a difference in this association between previous users and non-users of sunscreen. Activity differences based on messages characteristics were not observed. Finally, activity in a region of right dorsolateral PFC (dlPFC), which has been observed with counterargu-ing against persuasive messages, correlated negatively with future behavior. The current results suggest it is reasonable to use fNIRS to examine persuasion paradigms that go beyond what is possible in the MRI scanner environment.

Placebo effects are common in all areas of medicine and beyond and thus, are also present when ergogenic aids are used to enhance performance in athletes. While they usually are regarded as secondary and a nuisance in relation to... more

Placebo effects are common in all areas of medicine and beyond and thus, are also
present when ergogenic aids are used to enhance performance in athletes. While they usually
are regarded as secondary and a nuisance in relation to performance-improving nutritional
supplements, we here propose to utilize them to investigate central control mechanisms of athletic performance. Following a brief review of the current literature on placebo effects in sports,
we outline a research protocol designed to understand the neurobiological basis of endurance
performance, limiting factors and the integration of central and peripheral fatigue mechanisms.
A placebo response to ergogenic aids will be elicited to isolate and study both central and peripheral components of performance regulation.

An improved understanding of how the brain allocates mental resources as a function of task difficulty is critical for enhancing human performance. Functional near infrared spectroscopy (fNIRS) is a field-deployable optical brain... more

An improved understanding of how the brain allocates mental resources as a function of task difficulty is critical for enhancing human performance. Functional near infrared spectroscopy (fNIRS) is a field-deployable optical brain monitoring technology that provides a direct measure of cerebral blood flow in response to cognitive activity. We found that fNIRS was sensitive to variations in task difficulty in both real-life (flight simulator) and laboratory settings (tests measuring executive functions), showing increased concentration of oxygenated hemoglobin (HbO2) and decreased concentration of deoxygenated hemoglobin (HHb) in the prefrontal cortex as the tasks became more complex. Intensity of prefrontal activation (HbO2 concentration) was not clearly correlated to task performance. Rather, activation intensity shed insight on the level of mental effort, i.e., how hard an individual was working to accomplish a task. When combined with performance, fNIRS provided an estimate of the participants' neural efficiency, and this efficiency was consistent across levels of difficulty of the same task. Overall, our data support the suitability of fNIRS to assess the mental effort related to human operations and represents a promising tool for the measurement of neural efficiency in other contexts such as training programs or the clinical setting. Understanding the way the brain allocates mental resources according to the task demand is critically important for complex and high risk operational settings (e.g. piloting an aircraft, controlling air traffic, supervising a nuclear plant, etc.). The increase in mental workload in the face of a challenging task can lead to performance breakdown 1, 2 with potentially fatal consequences. Measuring mental workload is complex as it represents the interplay between the demands of the environment (input load), human characteristics (capacities), and task performance (output). Thus, taking into account solely the task characteristics does now allow inferring the level of mental workload in an individual. There are many classical neuroimaging methods that allow measuring the neural substrates of mental workload in a continuous and unobtrusive way, such as electroencepha-lography (EEG) 3 , functional magnetic resonance imaging (fMRI) 4 , and positron emission tomography (PET) 5. While these techniques have enabled an unprecedented window into the functioning of the human brain, they are not suited for use in ecological contexts. Indeed, EEG measures are subject to numerous artefacts due to head and/or body movements, and PET and fMRI require the subjects to lie supine and immobile during data acquisition. Therefore, there is a need for sensitive, continuous and robust measurements that are able to discriminate between various mental effort levels. Functional near infrared spectroscopy (fNIRS) is a relatively new and promising imaging technique that meets such measurement requirements, and the important advantage of being portable and field-deployable. This technique measures the oxygenated (HbO2) and deoxygenated (HHb) hemoglobin in the blood supply of the brain, and has been shown to discriminate between various mental effort levels (e.g. Ayaz et al. 6). In contrast to the more classical neuroimaging techniques, fNIRS allows in-vivo imaging in ecological conditions with natural freedom of movement and in complex environments such as high-fidelity flight simulators.

Music played in ensembles is a naturalistic model to study joint action and leader- follower relationships. Recently, the investigation of the brain underpinnings of joint musical actions has gained attention; however, the cerebral... more

Music played in ensembles is a naturalistic model to study joint action and leader- follower relationships. Recently, the investigation of the brain underpinnings of joint musical actions has gained attention; however, the cerebral correlates underlying the roles of leader and follower in music performance remain elusive. The present study addressed this question by simultaneously measuring the hemodynamic correlates of functional neural activity elicited during naturalistic violin duet performance using fNIRS. Findings revealed distinct patterns of functional brain activation when musicians played the Violin 2 (follower) than the Violin 1 part (leader) in duets, both compared to solo performance. More specifically, results indicated that musicians playing the Violin 2 part had greater oxy-Hb activation in temporo-parietal (p = 0.02) and somatomotor (p = 0.04) regions during the duo condition in relation to the solo. On the other hand, there were no significant differences in the activation of these areas between duo/solo conditions during the execution of the Violin 1 part (p’s > 0.05). These findings suggest that ensemble cohesion during a musical performance may impose particular demands when musicians play the follower position, especially in brain areas associated with the processing of dynamic social information and motor simulation. This study is the first to use fNIRS hyperscanning technology to simultaneously measure the brain activity of two musicians during naturalistic music ensemble performance, opening new avenues for the investigation of brain correlates underlying joint musical actions with multiple subjects in a naturalistic environment.

In this study we present a method of signal processing to determine dominant channels in near infrared spectroscopy (NIRS). To compare measuring channels and identify delays between them, cross correlation is computed. Furthermore, to... more

In this study we present a method of signal processing to determine dominant channels in near infrared spectroscopy (NIRS). To compare measuring channels and identify delays between them, cross correlation is computed. Furthermore, to find out possible dominant channels, a visual inspection was performed. The outcomes demonstrated that the visual inspection exhibited evoked-related activations in the primary somatosensory cortex (S1) after stimulation which is consistent with comparable studies and the cross correlation study discovered dominant channels on both cerebral hemispheres. The analysis also showed a relationship between dominant channels and adjacent channels. For that reason, our results present a new method to identify dominant regions in the cerebral cortex using near-infrared spectroscopy. These findings have also implications in the decrease of channels by eliminating irrelevant channels for the experiment.

In this paper we present the use of a signal processing technique to find dominant channels in near infrared spectroscopy (NIRS). Cross correlation is computed to compare measuring channels and identify delays among the channels. In... more

In this paper we present the use of a signal processing technique to find dominant channels in near infrared spectroscopy (NIRS). Cross correlation is computed to compare measuring channels and identify delays among the channels. In addition, visual inspection was used to detect potential dominant channels. The results showed that the visual analysis exposed pain-related activations in the primary somatosensory cortex (S1) after stimulation which is consistent with similar studies and the cross correlation analysis found dominant channels on both cerebral hemispheres. The analysis also showed a relationship between dominant channels and neighbouring channels. Therefore, our results present a new method to detect dominant regions in the cerebral cortex using near-infrared spectroscopy. These results have also implications in the reduction of number of channels by eliminating irrelevant channels for the experiment.

Researchers have found that deaf children’s early exposure to a visual sign language and its visual sign phonological-syllabic structure promotes success in reading English. However, little is known about the multitude of visual cues to... more

Researchers have found that deaf children’s early exposure to a visual sign language and its visual sign phonological-syllabic structure promotes success in reading English. However, little is known about the multitude of visual cues to which deaf children attend when learning to read. Nothing is known about the relative weighting of these visual cues, nor what processing principles underlie deaf children’s decoding of meaning from print. How does the young deaf reader allocate attention to, and process, linguistic sign phonological-syllabic cues (one key cue being fingerspelling, a manual representation of English orthography), orthographic text-based print cues, and nonlinguistic meaningful images on the page? From the perspective of brain development and neural plasticity, do differences in the age of language exposure (AoE) impact visual attention, allocation, and processing of text in the emergent reader?

After 800,000 years of making simple Oldowan tools, early humans began manufacturing Acheulian handaxes around 1.75 million years ago. This advance is hypothesized to reflect an evolutionary change in hominin cognition and language... more

After 800,000 years of making simple Oldowan tools, early humans began manufacturing Acheulian handaxes around 1.75 million years ago. This advance is hypothesized to reflect an evolutionary change in hominin cognition and language abilities. We used a neuroarchaeology approach to investigate this hypothesis, recording brain activity using functional near-infrared spectroscopy as modern human participants learned to make Oldowan and Acheulian stone tools in either a verbal or nonverbal training context. Here we show that Acheulian tool production requires the integration of visual, auditory and sensorimotor information in the middle and superior temporal cortex, the guidance of visual working memory representations in the ventral precentral gyrus, and higher-order action planning via the supplementary motor area, activating a brain network that is also involved in modern piano playing. The right analogue to Broca’s area—which has linked tool manufacture and language in prior work1,2...

The wide-ranging manipulations to the cardiovascular system that frequently occur during cardiac surgery can expose the brain to variations in its blood supply that could prove deleterious. As a first step to developing a resource... more

The wide-ranging manipulations to the cardiovascular system that frequently occur during cardiac surgery can expose the brain to variations in its blood supply that could prove deleterious. As a first step to developing a resource suitable for monitoring such changes, we detected the hemodynamic events induced in the brain of a primate model, using high-density near-infrared spectroscopy combined with tomographic reconstruction methods and validated the findings using established radiologic and histologic techniques. Continuous monitoring of the relative changes in the components of the cerebral hemoglobin signal was performed using high-density near-infrared spectroscopy (270 source-detector channel array) in anesthetized bonnet macaques with the brain exposed to induced ischemia and other acute events. A comparative analysis (exact binomial test) applied to reconstructed 3-dimensional images before and after the events and between cerebral hemispheres, combined with postprocedure ...

Researchers from multiple fields have sought to understand how sex moderates human social behavior. While over 50 years of research has revealed differences in cooperation behavior of males and females, the underlying neural correlates of... more

Researchers from multiple fields have sought to understand how sex moderates human social behavior. While over 50 years of research has revealed differences in cooperation behavior of males and females, the underlying neural correlates of these sex differences have not been explained. A missing and fundamental element of this puzzle is an understanding of how the sex composition of an interacting dyad influences the brain and behavior during cooperation. Using fNIRS-based hyperscanning in 111 same- and mixed-sex dyads, we identified significant behavioral and neural sex-related differences in association with a computer-based cooperation task. Dyads containing at least one male demonstrated significantly higher behavioral performance than female/female dyads. Individual males and females showed significant activation in the right frontopolar and right inferior prefrontal cortices, although this activation was greater in females compared to males. Female/female dyad’s exhibited significant inter-brain coherence within the right temporal cortex, while significant coherence in male/male dyads occurred in the right inferior prefrontal cortex. Significant coherence was not observed in mixed-sex dyads. Finally, for same-sex dyads only, task-related inter-brain coherence was positively correlated with cooperation task performance. Our results highlight multiple important and previously undetected influences of sex on concurrent neural and behavioral signatures of cooperation.

Functional Near-Infrared Spectroscopy (fNIRS) is a non-invasive imaging method that allows measuring hemodynamic changes at the cortical level. Functional NIRS has gained interest as a potential alternative to fMRI given the high... more

Functional Near-Infrared Spectroscopy (fNIRS) is a non-invasive imaging method that allows measuring hemodynamic changes at the cortical level. Functional NIRS has gained interest as a potential alternative to fMRI given the high correlation between Oxyhemoglobin (HbO) changes
recorded using fNIRS and the fMRI BOLD signal that reflects the differential between Oxygenated and Deoxygenated hemoglobin, i.e HbT. Furthermore, fNIRS features facility and flexibility of use combined with safety, making it a versatile tool. In the present study, we examined brain activity associated with the updating process in working memory using a N-back paradigm. Working memory reflects the ongoing, active maintenance and manipulation of limited amounts of information. Cortical brain activity was recorded in 12 young healthy adults using a multichannel fNIRS system (BrainSight, v2.3b12). Oxy- and deoxy-hemodynamic activity, as estimated by changes in light diffusion attenuation, was measured at two wavelengths: 685 and 830 nm. The configuration of the optodes featured 8 sources and 16 detectors, clustered over four main areas, i.e. the prefrontal and parietal regions in the left and right hemispheres. Continuous signals were digitalized at a sample rate of 10 Hz, and the spatial position of optodes was accurately set up using a 3-D coordinates system coupled with a Polaris localization system. Data analysis was computed off-line using the Matlab (V.11) programming environment and HOmer toolbox (3). During the experimental procedure, participants were presented with an alternative succession of two conditions, repeated 5 times. In both conditions, letters were successively displayed on screen. In the easiest (N0) condition, participants had simply to press a key each time the letter "X" was presented. In the updating working memory condition (N2), participants were instructed to press the key only when the letter displayed on the screen was the same that the letter presented two positions before. Higher cognitive demands in the N2 than the N0 condition, associated with higher updating demands should be related with increased brain activity in key areas. Accordingly, preliminary results disclosed increased HbO levels during the working memory task (N2 > N0), especially in parietal cortices. These results are in agreement with a growing literature that propose fNIRS as a suitable and pragmatic mechanism to study brain activity related to working memory paradigms.

Early bilingual exposure, especially exposure to two languages in different modalities such as speech and sign, can profoundly affect an individual’s language, culture, and cognition. Here we explore the hypothesis that bimodal dual... more

Early bilingual exposure, especially exposure to two languages in different modalities such as speech and sign, can profoundly affect an individual’s language, culture, and cognition. Here we explore the hypothesis that bimodal dual language exposure can also affect the brain’s organization for language. These changes occur across brain regions universally important for language and parietal regions especially critical for sign language (Newman et al., 2002). We investigated three groups of participants (N = 29) that completed a word repetition task in American Sign Language (ASL) during fNIRS brain imaging. Those groups were (1) hearing ASL-English bimodal bilinguals (n = 5), (2) deaf ASL signers (n = 7), and (3) English monolinguals naïve to sign language (n = 17). The key finding of the present study is that bimodal bilinguals showed reduced activation in left parietal regions relative to deaf ASL signers when asked to use only ASL. In contrast, this group of bimodal signers showed greater activation in left temporo-parietal regions relative to English monolinguals when asked to switch between their two languages (Kovelman et al., 2009). Converging evidence now suggest that bimodal bilingual experience changes the brain bases of language, including the left temporo-parietal regions known to be critical for sign language processing (Emmorey et al., 2007). The results provide insight into the resilience and constraints of neural plasticity for language and bilingualism.

An improved understanding of how the brain allocates mental resources as a function of task difficulty is critical for enhancing human performance. Functional near infrared spectroscopy (fNIRS) is a field-deployable optical brain... more

An improved understanding of how the brain allocates mental resources as a function of task difficulty is critical for enhancing human performance. Functional near infrared spectroscopy (fNIRS) is a field-deployable optical brain monitoring technology that provides a direct measure of cerebral blood flow in response to cognitive activity. We found that fNIRS was sensitive to variations in task difficulty in both real-life (flight simulator) and laboratory settings (tests measuring executive functions), showing increased concentration of oxygenated hemoglobin (HbO2) and decreased concentration of deoxygenated hemoglobin (HHb) in the prefrontal cortex as the tasks became more complex. Intensity of prefrontal activation (HbO2 concentration) was not clearly correlated to task performance. Rather, activation intensity shed insight on the level of mental effort, i.e., how hard an individual was working to accomplish a task. When combined with performance, fNIRS provided an estimate of the...

The aim of this study was to investigate how test methods affect listening test takers' performance and cognitive load. Test methods were defined and operationalized as whilelistening performance (WLP) and post-listening performance (PLP)... more

The aim of this study was to investigate how test methods affect listening test takers' performance and cognitive load. Test methods were defined and operationalized as whilelistening performance (WLP) and post-listening performance (PLP) formats. To achieve the goal of the study, we examined test takers' (N = 80) brain activity patterns (measured by functional near-infrared spectroscopy (fNIRS)), gaze behaviors (measured by eye-tracking), and listening performance (measured by test scores) across the two test methods. We found that the test takers displayed lower activity levels across brain regions supporting comprehension during the WLP tests relative to the PLP tests. Additionally, the gaze behavioral patterns exhibited during the WLP tests suggested that the test takers adopted keyword matching and "shallow listening." Together, the neuroimaging and gaze behavioral data indicated that the WLP tests imposed a lower cognitive load on the test takers than the PLP tests. However, the test takers performed better with higher test scores for one of two WLP tests compared with the PLP tests. By incorporating eye-tracking and neuroimaging in this exploration, this study has advanced the current knowledge on cognitive load and the impact imposed by different listening test methods. To advance our knowledge of test validity, other researchers could adopt our research protocol and focus on extending the test method framework used in this study.

The wide-ranging manipulations to the cardiovascular system that frequently occur during cardiac surgery can expose the brain to variations in its blood supply that could prove deleterious. As a first step to developing a resource... more

The wide-ranging manipulations to the cardiovascular system that frequently occur during cardiac surgery can expose the brain to variations in its blood supply that could prove deleterious. As a first step to developing a resource suitable for monitoring such changes, we detected the hemodynamic events induced in the brain of a primate model, using high-density near-infrared spectroscopy combined with tomographic reconstruction methods and validated the findings using established radiologic and histologic techniques. Continuous monitoring of the relative changes in the components of the cerebral hemoglobin signal was performed using high-density near-infrared spectroscopy (270 source-detector channel array) in anesthetized bonnet macaques with the brain exposed to induced ischemia and other acute events. A comparative analysis (exact binomial test) applied to reconstructed 3-dimensional images before and after the events and between cerebral hemispheres, combined with postprocedure ...

Functional near infrared spectroscopy (fNIRS) is a clinically feasible functional neuroimaging modality for detecting early cortical changes due to neurodegenerative diseases that affect cognition. The objective of this preliminary... more

Functional near infrared spectroscopy (fNIRS) is a clinically feasible functional neuroimaging modality for detecting early cortical changes due to neurodegenerative diseases that affect cognition. The objective of this preliminary investigation was to test for reduced prefrontal activity in persons with cognitive impairments due to amyotrophic lateral sclerosis (ALS). Participants were required to complete two N-back working memory tasks of increasing complexity during fNIRS recordings. Five participants with ALS and age- and gender-matched healthy participants comprised the experimental and control groups, respectively. Significant reductions in prefrontal oxygenation levels were observed for the left and right hemispheres in the ALS group compared to the control group. Reduced prefrontal activation despite intact behavioral performance for a working memory task may suggest early neuroanatomical, neurophysiological and/or compensatory mechanisms in affected individuals. The fNIRS-derived oxygenation measure shows promise as a sensitive neural marker to identify early neuropsychological impairments due to ALS.

Cortical spreading depression (CSD) leads to dramatic changes in cerebral hemodynamics. However, mechanisms involved in promoting and counteracting cerebral vasodilator responses are unclear. Here we review the development and current... more

Cortical spreading depression (CSD) leads to dramatic changes in cerebral hemodynamics. However, mechanisms involved in promoting and counteracting cerebral vasodilator responses are unclear. Here we review the development and current status of this important field of research especially with respect to the role of perivascular nerves and nitric oxide (NO). It appears that neurotransmitters released from the sensory and the parasympathetic nerves associated with cerebral arteries, and NO released from perivascular nerves and/or parenchyma, promote cerebral hyperemia during CSD. However, the relative contributions of each of these factors vary according to species studied. Related to CSD, axonal and reflex responses involving trigeminal afferents on the pial surface lead to increased blood flow and inflammation of the overlying dura mater. Counteracting the cerebral vascular dilation is the production and release of constrictor prostaglandins, at least in some species, and other poss...

Nowadays, brain function evaluation using Functional Near Infrared Spectroscopy (fNIRS) is one of the most potential non-invasive monitoring techniques. This paper concerns usefulness of the NIRS signals denoising using the Hemodynamic... more

Nowadays, brain function evaluation using Functional Near Infrared Spectroscopy (fNIRS) is one of the most potential non-invasive monitoring techniques. This paper concerns usefulness of the NIRS signals denoising using the Hemodynamic Evoked Response (HomER) as graphical user interface displays the NIRS data, fast independent component analysis (FASTICA) method to reduce data dimension and the combined Wavelet & PCA method for enhancing NIRS signals. NIRS signals include many types of noise, spread across a broad spectrum of frequencies, such as: low frequency noise from respiratory interference, 0.1 - 0.3 Hz, Mayer wave, about 0.1 Hz, cardiac interference, 0.8 - 2.0 Hz, and other artifacts from head and facial motions. Meanwhile, electronic components generate high frequency noise. Multi-resolution wavelet and PCA was applied successfully to enhance the NIRS signals. It consists of adaptively modifying the wavelet coefficients based on the degree of noise contamination of the processed NIRS signal. This is done subsequently to the signal pre-processing by reducing data dimension using the FASTICA method. We demonstrate, using signal-to-noise ratio and correlation indicators, that the technique used is superior to the wavelet and moving average filter and outperforms the proposed denoising NIRS signal.

Individual differences in the temporal dynamics of the haemodynamic response can reflect cortical excitation and can reveal underlying cortical physiology. Here, we show differences in the shape of the haemodynamic response that are... more

Individual differences in the temporal dynamics of the haemodynamic response can reflect cortical excitation and can reveal underlying cortical physiology. Here, we show differences in the shape of the haemodynamic response that are dependent on stimulus parameters. Two sets of visual stimuli were used varying in parameters that are known to manipulate the haemodynamic response in the visual cortex. We measured the oxyhaemoglobin response using near infrared spectroscopy. The first set of stimuli comprised chromatic square-wave gratings that varied with respect to the separation in the CIE UCS chromaticities of the alternating bars. The gratings with large separations in chromaticity evoked an oxyhaemoglobin response with greater amplitude, consistent with greater activation of the visual cortex. The second set of stimuli comprised horizontal achromatic gratings that (1) were static, (2) drifted at a constant velocity towards fixation, or (3) reversed direction every half spatial cycle to create a vertical vibrating motion. Although the three types of grating had a similar effect on the amplitude of the oxyhaemoglobin response, the moving gratings (2 and 3) evoked a steeper decrease in oxyhaemoglobin concentration after stimulus-offset. The steeper slope appears to reflect the post-stimulus undershoot and the slope may provide a correlate of cortical excitability when the amplitude of the haemodynamic response has saturated.

Erin Treacy Solovey1, Francine Lalooses1, Krysta Chauncey1, Douglas Weaver1, Margarita Parasi1, Matthias Scheutz1, Angelo Sassaroli2, Sergio Fantini2, Paul Schermerhorn3, Audrey Girouard4, Robert JK Jacob1 1Tufts University Computer... more

Erin Treacy Solovey1, Francine Lalooses1, Krysta Chauncey1, Douglas Weaver1, Margarita Parasi1, Matthias Scheutz1, Angelo Sassaroli2, Sergio Fantini2, Paul Schermerhorn3, Audrey Girouard4, Robert JK Jacob1 1Tufts University Computer Science 161 College Ave., ...