Human Face Perception Using Electroencephalography and Magnetoencephalography.

The face has a large amount of information that is useful for humans in social communication. Recently, non-invasive methods have been used to investigate human brain activity related to perception and cognition processes. Electroencephalography (EEG) and magnetoencephalography (MEG) have excellent temporal resolution and reasonably good spatial resolution. Therefore, they are useful to investigate time sequences of human brain activity related to the face perception process. In this review, we introduce our previous EEG and MEG studies of human face perception that demonstrated the following characteristics of face perception processing: (1) Event-related components in the temporal area related to the activity in the inferior temporal (IT) area, corresponding to the fusiform face area (FFA), are evoked approximately 180 msec after the presentation of a face. The activity in the IT area plays an important role in the detection processing of a face, and the contours of a face affect the activity in the IT areas. (2) Event-related components in the temporal area related to the superior temporal sulcus (STS) activity are larger when eyes are averted than when directly looking into the eyes. (3) The direction of features of a face affects the face perception processing in the right hemisphere. On the other hand, the matching of the direction between the contours and features of a face affects the processing in the left hemisphere. (4) Random dots blinking (RDB), which uses temporal changes in patterns of many small dots to present stimuli without a change in luminance during the presentation of a face, is a useful visual stimulus method to investigate the brain activity related to face perception processing in the IT area using EEG and MEG.

The ERP and psychophysical changes related to facial emotion perception by expertise in Japanese hospitality, "OMOTENASHI".

We investigated the emotion perception process based on hospitality expertise. Forty subjects were divided into the OMOTENASHI group working at inns considered to represent the spirit of hospitality, OMOTENASHI in Japan, and CONTROL group without experience in the hospitality industry. We presented neutral, happy, and angry faces to investigate P100 and N170 by these faces, and psychophysical changes by the favor rating test to evaluate emotional perception. In the favor rating test, the score was significantly smaller (less favorable) in OMOTENASHI than in CONTROL. Regarding event-related potential components, the maximum amplitude of P100 was significantly larger for a neutral face at the right occipital electrode in OMOTENASHI than in CONTROL, and it was significantly larger for an angry face at both occipital electrodes in OMOTENASHI than in CONTROL. However, the peak latency and maximum amplitude of N170 were not significantly different between OMOTENASHI and CONTROL at both temporal electrodes for each emotion condition. Differences on the favor rating test and P100 in OMOTENASHI suggested that workers at inns may more quickly notice and be more sensitive to the facial emotion of guests due to hospitality training, and/or that hospitality expertise may increase attention to emotion by top-down and/or bottom-up processing.

Neural representation of feature synergy.

Interactive non-linear cooperation of different feature dimensions, feature synergy, has been studied in psychophysics, but the neural mechanism is unknown. The present study investigated the neural representation of feature synergy of two second-order visual features by combining electroencephalography (EEG) with the signal detection theory (SDT). Two kinds of a 27-by-27 array of Gabor patches were presented in a random order; a reference stimulus which has no segregated region, and a target stimulus whose inner region differed in spatial frequency, orientation, or both from the surround. Subjects performed a Yes-No discrimination of whether the inner region was different from the surround, while EEG signals were recorded from 62 locations. When the SDT measure showed feature synergy, EEG activity showed a long-lasting enhancement starting at 130 ms around the inferior temporal region. In contrast, no EEG modulation was observed when feature synergy was not present. Thus, our combined approach demonstrates that non-linear cooperation between different features is represented by neural activity starting at 130 ms post-stimulus in the ventral visual stream.

Non-linear laws of echoic memory and auditory change detection in humans.

BACKGROUND: The detection of any abrupt change in the environment is important to survival. Since memory of preceding sensory conditions is necessary for detecting changes, such a change-detection system relates closely to the memory system. Here we used an auditory change-related N1 subcomponent (change-N1) of event-related brain potentials to investigate cortical mechanisms underlying change detection and echoic memory. RESULTS: Change-N1 was elicited by a simple paradigm with two tones, a standard followed by a deviant, while subjects watched a silent movie. The amplitude of change-N1 elicited by a fixed sound pressure deviance (70 dB vs. 75 dB) was negatively correlated with the logarithm of the interval between the standard sound and deviant sound (1, 10, 100, or 1000 ms), while positively correlated with the logarithm of the duration of the standard sound (25, 100, 500, or 1000 ms). The amplitude of change-N1 elicited by a deviance in sound pressure, sound frequency, and sound location was correlated with the logarithm of the magnitude of physical differences between the standard and deviant sounds. CONCLUSIONS: The present findings suggest that temporal representation of echoic memory is non-linear and Weber-Fechner law holds for the automatic cortical response to sound changes within a suprathreshold range. Since the present results show that the behavior of echoic memory can be understood through change-N1, change-N1 would be a useful tool to investigate memory systems.

Echoic memory of a single pure tone indexed by change-related brain activity.

BACKGROUND: The rapid detection of sensory change is important to survival. The process should relate closely to memory since it requires that the brain separate a new stimulus from an ongoing background or past event. Given that sensory memory monitors current sensory status and works to pick-up changes in real-time, any change detected by this system should evoke a change-related cortical response. To test this hypothesis, we examined whether the single presentation of a sound is enough to elicit a change-related cortical response, and therefore, shape a memory trace enough to separate a subsequent stimulus. RESULTS: Under a paradigm where two pure sounds 300 ms in duration and 800 or 840 Hz in frequency were presented in a specific order at an even probability, cortical responses to each sound were measured with magnetoencephalograms. Sounds were grouped to five events regardless of their frequency, 1D, 2D, and 3D (a sound preceded by one, two, or three different sounds), and 1S and 2S (a sound preceded by one or two same sounds). Whereas activation in the planum temporale did not differ among events, activation in the superior temporal gyrus (STG) was clearly greater for the different events (1D, 2D, 3D) than the same event (1S and 2S). CONCLUSIONS: One presentation of a sound is enough to shape a memory trace for comparison with a subsequent physically different sound and elicits change-related cortical responses in the STG. The STG works as a real-time sensory gate open to a new event.

Effect of configural distortion on a face-related ERP evoked by random dots blinking.

Using random dots blinking (RDB), which reflects the activity of the higher visual area related to face perception, the following stimuli were presented. (1) Upright: a schematic face; (2) Inverted: the Upright stimulus inverted; and (3) Scrambled: the same contour and features as in Upright but with the spatial relation distorted. Clear negative components (N-ERP250) were identified at approximately 250 ms after stimulus onset. At the T5 and T6 electrodes, the peak latency was significantly longer for Inverted and Scrambled than for Upright. At the P4 electrode, the maximum amplitude was significantly larger for Scrambled than for Upright and Inverted. These results indicate that the delayed latency for Inverted and Scrambled reflects the involvement of the additional analytic processing caused by the configural distortion, and that the increase in amplitude for Scrambled indicates the existence of further processing caused by the distortion of the spatial relationship between the contour and features.

A transition from unimodal to multimodal activations in four sensory modalities in humans: an electrophysiological study.

BACKGROUND: To investigate the long-latency activities common to all sensory modalities, electroencephalographic responses to auditory (1000 Hz pure tone), tactile (electrical stimulation to the index finger), visual (simple figure of a star), and noxious (intra-epidermal electrical stimulation to the dorsum of the hand) stimuli were recorded from 27 scalp electrodes in 14 healthy volunteers. RESULTS: Results of source modeling showed multimodal activations in the anterior part of the cingulate cortex (ACC) and hippocampal region (Hip). The activity in the ACC was biphasic. In all sensory modalities, the first component of ACC activity peaked 30-56 ms later than the peak of the major modality-specific activity, the second component of ACC activity peaked 117-145 ms later than the peak of the first component, and the activity in Hip peaked 43-77 ms later than the second component of ACC activity. CONCLUSION: The temporal sequence of activations through modality-specific and multimodal pathways was similar among all sensory modalities.

Priority of face perception during subliminal stimulation using a new color-opponent flicker stimulation.

We developed a new method of color-opponent flicker (COF) stimulation, and investigated behavioral responses for object discrimination at the around threshold frequency of COF stimulation. Pairs of figures, a face, flower, the letter "G" and a random pattern, were drawn with a red and green checkerboard with a black mesh. COF stimulation was produced by presenting pairs of figures alternately (red-green-red-green-) at various frequencies (30-120 Hz). A discrimination task for objects during COF stimulation was performed by 16 healthy subjects. Threshold frequency of COF stimulation was between 50 and 75 Hz. The accuracy rate for face discrimination was significantly higher than those for other objects (p<0.01, ANOVA with Fisher's PLSD multiple comparisons test). The present COF stimulation technique could be useful to investigate subliminal processes of the visual system, and the present results indicate a higher sensitivity and selectivity for face discrimination than those for other objects.

Differential age-related changes in N170 responses to upright faces, inverted faces, and eyes in Japanese children.

The main objectives of this study were to investigate the development of face perception in Japanese children, focusing on the changes in face processing strategies (holistic and/or configural vs. feature-based) that occur during childhood. To achieve this, we analyzed the face-related N170 component, evoked by upright face, inverted face, and eyes stimuli in 82 Japanese children aged between 8- and 13-years-old. During the experiment, the children were asked to perform a target detection task in which they were told to press a button when they saw images of faces or kettles with mustaches, glasses, and fake noses; i.e., an implicit face perception task. The N170 signals observed after the presentation of the upright face stimuli were longer in duration and/or had at least two peaks in the 8-11-year-old children, whereas those seen in the 12-13-year-old children were sharp and only had a single peak. N170 latency was significantly longer after the presentation of the eyes stimuli than after the presentation of the upright face stimuli in the 10- and 12-year-old children. In addition, significant differences in N170 latency were observed among all three stimulus types in the 13-year-old children. N170 amplitude was significantly greater after the presentation of the eyes stimuli than after the presentation of the upright face stimuli in the 8-10- and 12-year-old children. The results of the present study indicate that the upright face stimuli were processed using holistic and/or configural processing by the 13-year-old children.

Brain responses for the subconscious recognition of faces.

We investigated the event-related responses following subthreshold and suprathreshold stimulation with facial and non-facial figures using magnetoencephalography (MEG) and EEG recordings to clarify the physiological nature of subconscious perception. Event-related magnetic fields and potentials were recorded from the right hemisphere in eight healthy subjects. Three types of stimulus, i.e., facial image (Face), letters of the alphabet (Letters) and random patterns of dots (Dots), with different presentation periods, subthreshold (16 ms), intermediate (32 ms) and suprathreshold (48 ms) were visually presented in a random order. A psychological discrimination task using the same stimuli was also employed. Clear MEG and EEG responses were recorded for all the stimuli, but the amplitude of the responses was largest for Face and smallest for Dots even in the subthreshold stimulation. The equivalent current dipoles (ECDs) for Face were located around the fusiform gyrus, although the correlation coefficients for ECDs were low under subthreshold and intermediate conditions. The ECDs for Letters and Dots were not estimated with reliable correlation coefficients. The results from the psychological task correlated with the dominancy of face recognition. Face perception was processed differently in the subthreshold condition as well as suprathreshold condition. The subconscious recognition of face might be processed around the fusiform gyrus.

Effects of inverting contour and features on processing for static and dynamic face perception: an MEG study.

We investigated the effects of inverting facial contour (hair and chin) and features (eyes, nose and mouth) on processing for static and dynamic face perception using magnetoencephalography (MEG). We used apparent motion, in which the first stimulus (S1) was replaced by a second stimulus (S2) with no interstimulus interval and subjects perceived visual motion, and presented three conditions as follows: (1) U&U: Upright contour and Upright features, (2) U&I: Upright contour and Inverted features, and (3) I&I: Inverted contour and Inverted features. In static face perception (S1 onset), the peak latency of the fusiform area's activity, which was related to static face perception, was significantly longer for U&I and I&I than for U&U in the right hemisphere and for U&I than for U&U and I&I in the left. In dynamic face perception (S2 onset), the strength (moment) of the occipitotemporal area's activity, which was related to dynamic face perception, was significantly larger for I&I than for U&U and U&I in the right hemisphere, but not the left. These results can be summarized as follows: (1) in static face perception, the activity of the right fusiform area was more affected by the inversion of features while that of the left fusiform area was more affected by the disruption of the spatial relation between the contour and features, and (2) in dynamic face perception, the activity of the right occipitotemporal area was affected by the inversion of the facial contour.

The development of the perception of facial emotional change examined using ERPs.

OBJECTIVE: The development of the perception of changes in facial emotion was investigated using event-related potentials (ERPs) in children and adults. METHODS: Four different conditions were presented: (1) N-H: a neutral face that suddenly changed to a happy face. (2) H-N: reverse of N-H. (3) N-A: a neutral face that suddenly changed to an angry face. (4) A-N: reverse of N-A. RESULTS: In the bilateral posterior temporal areas, a negative component was evoked by all conditions in younger children (7-10 years old), older children (11-14 years old), and adults (23-33 years old) within 150-300 ms. Peak latency was significantly shorter and amplitude was significantly smaller in adults than younger and older children. Moreover, maximum amplitude was significantly larger for N-H and N-A than H-N and A-N in younger children and for N-H than the other three conditions in adults. CONCLUSION: The areas of the brain involved in perceiving changes in facial emotion have not matured by 14 years of age. SIGNIFICANCE: Our study is the first to clarify a difference between children and adults in the perception of facial emotional change.

Assessing Aδ fiber function with lidocaine using intraepidermal electrical stimulation.

UNLABELLED: The functions of small fibers can be impaired in peripheral neuropathies, and screening tests for clinical use are required. To verify whether intraepidermal stimulation (IES) is useful for assessing the functions of Adelta fibers in the superficial layer, we investigated sensory thresholds and evoked cortical responses in healthy volunteers before and after a transdermal administration of lidocaine. Pain and tactile thresholds were studied using IES and transcutaneous electrical stimulation (TS), respectively, in 10 healthy volunteers before, and 1 hour, 3 hours, and 5 hours after a local anesthesia with lidocaine. Cortical potentials evoked with IES and TS were also studied in 12 healthy volunteers before and 5 hours after the anesthesia. Although the local anesthesia had no effect on the evoked potentials or the tactile threshold for TS, it markedly increased the pain threshold and almost abolished the evoked potentials for IES. These results suggest that IES is a sensitive tool for detecting functional changes of cutaneous Adelta fibers. PERSPECTIVE: Compared with other methods of stimulation used to investigate Adelta fiber function, our method is easy to apply and less invasive and can stimulate any site of the body. Therefore, it should be useful as a screening test for patients with neuropathy.

Event-related potentials of self-face recognition in children with pervasive developmental disorders.

Patients with pervasive developmental disorders (PDD) often have difficulty reading facial expressions and deciphering their implied meaning. We focused on semantic encoding related to face cognition to investigate event-related potentials (ERPs) to the subject's own face and familiar faces in children with and without PDD. Eight children with PDD (seven boys and one girl; aged 10.8+/-2.9 years; one left-handed) and nine age-matched typically developing children (four boys and five girls; aged 11.3+/-2.3 years; one left-handed) participated in this study. The stimuli consisted of three face images (self, familiar, and unfamiliar faces), one scrambled face image, and one object image (e.g., cup) with gray scale. We confirmed three major components: N170 and early posterior negativity (EPN) in the occipito-temporal regions (T5 and T6) and P300 in the parietal region (Pz). An enhanced N170 was observed as a face-specific response in all subjects. However, semantic encoding of each face might be unrelated to N170 because the amplitude and latency were not significantly different among the face conditions. On the other hand, an additional component after N170, EPN which was calculated in each subtracted waveform (self vs. familiar and familiar vs. unfamiliar), indicated self-awareness and familiarity with respect to face cognition in the control adults and children. Furthermore, the P300 amplitude in the control adults was significantly greater in the self-face condition than in the familiar-face condition. However, no significant differences in the EPN and P300 components were observed among the self-, familiar-, and unfamiliar-face conditions in the PDD children. The results suggest a deficit of semantic encoding of faces in children with PDD, which may be implicated in their delay in social communication.

Differential priming effects of color-opponent subliminal stimulation on visual magnetic responses.

We investigated the effects of subliminal stimulation on visible stimulation to demonstrate the priority of facial discrimination processing, using a unique, indiscernible, color-opponent subliminal (COS) stimulation. We recorded event-related magnetic cortical fields (ERF) by magnetoencephalography (MEG) after the presentation of a face or flower stimulus with COS conditioning using a face, flower, random pattern, and blank. The COS stimulation enhanced the response to visible stimulation when the figure in the COS stimulation was identical to the target visible stimulus, but more so for the face than for the flower stimulus. The ERF component modulated by the COS stimulation was estimated to be located in the ventral temporal cortex. We speculated that the enhancement was caused by an interaction of the responses after subthreshold stimulation by the COS stimulation and the suprathreshold stimulation after target stimulation, such as in the processing for categorization or discrimination. We also speculated that the face was processed with priority at the level of the ventral temporal cortex during visual processing outside of consciousness.

Tonotopic representation of missing fundamental complex sounds in the human auditory cortex.

The N1m component of the auditory evoked magnetic field in response to tones and complex sounds was examined in order to clarify whether the tonotopic representation in the human secondary auditory cortex is based on perceived pitch or the physical frequency spectrum of the sound. The investigated stimulus parameters were the fundamental frequencies (F0 = 250, 500 and 1000 Hz), the spectral composition of the higher harmonics of the missing fundamental sounds (2nd to 5th, 6th to 9th and 10th to 13th harmonic) and the frequencies of pure tones corresponding to F0 and to the lowest component of each complex sound. Tonotopic gradients showed that high frequencies were more medially located than low frequencies for the pure tones and for the centre frequency of the complex tones. Furthermore, in the superior-inferior direction, the tonotopic gradients were different between pure tones and complex sounds. The results were interpreted as reflecting different processing in the auditory cortex for pure tones and complex sounds. This hypothesis was supported by the result of evoked responses to complex sounds having longer latencies. A more pronounced tonotopic representation in the right hemisphere gave evidence for right hemispheric dominance in spectral processing.