Taisuke Nakashima

Early ERP components differentially extract facial features: evidence for spatial frequency-and-contrast detectors.

It is generally accepted that the N170 component of an event-related potential (ERP) reflects the structural encoding of faces and is specialized for face processing. Recent neuroimaging and ERP studies have demonstrated that spatial frequency is a crucial factor for face recognition. To clarify which early ERP components reflect either coarse (low spatial frequency, LSF) or fine (high spatial frequency, HSF) processing of faces, we recorded ERPs induced by manipulated face stimuli. By filtering the original grayscale faces (broadband spatial frequency) spatially, we created LSF and HSF face stimuli. Next, we created physically equiluminant (PEL) face stimuli to eliminate the effects of lower order information, such as luminance and contrast. The P1 amplitude at the occipital region was augmented by LSF faces, while the N170 amplitude increased for HSF faces. The occipital P1 amplitude for PEL faces was relatively unaffected compared with that for PEL houses. In addition, the occipital N2 for PEL faces was spatiotemporally separable from N170 in a time-window between P1 and N170. These results indicate that P1 reflects coarse processing of faces, and that the face robustness further assures face-specific processing in the early component. Moreover, N2 reflects the early contrast processing of faces whereas N170 analyzes the fine facial features. Our findings suggest the presence of spatial frequency-and-contrast detectors for face processing.

Decreased spatial frequency sensitivities for processing faces in male patients with chronic schizophrenia

OBJECTIVE Schizophrenia impairs early visual cognitive processing. Low and high spatial frequency (LSF, HSF) visual information are differentially processed in humans. We investigated whether electrophysiological abnormalities exist in visual processing for spatial frequency (SF)-filtered neutral/emotional faces in schizophrenics. METHODS Subjects consisted of 16 male chronic schizophrenics and 23 controls. Event-related potentials (ERPs) to SF-filtered (LSF or HSF) and unfiltered (broad SF; BSF) pictures of neutral, happy, and fearful faces were recorded at 20 scalp sites. The relationships between the P100 (P1)/N170 amplitudes and the Global Assessment of Functioning (GAF) scores in patients were also evaluated. RESULTS For the P1 amplitudes at O1/O2, controls exhibited a significant LSF>BSF difference, while schizophrenics showed no LSF>BSF difference. For the N170 amplitudes at T5/T6, controls revealed a significant HSF>BSF difference, while schizophrenics showed no such difference. For the P1 latencies, controls but not schizophrenics showed a significant difference (LSF>BSF=HSF). For the N170 latencies, no significant SF differentiation was found between the two groups. For both P1 and N170 amplitudes, no significant effects of facial expressions were observed in controls and patients regardless of SFs. There were significant negative correlations between the GAF scores and the N170 amplitudes to BSF faces in schizophrenics, but not for P1 amplitudes. CONCLUSIONS Schizophrenics showed abnormal P1 and N170 responses to SF changes in faces, thus indicating decreased SF sensitivities for processing of faces. SIGNIFICANCE Abnormal early visual processing may underlie some of the deficits associated with face recognition in schizophrenia.

Electrophysiological evidence for sequential discrimination of positive and negative facial expressions

OBJECTIVE To elucidate the differences in temporal processing between positive and negative facial expressions by using event-related potentials (ERPs) with spatially filtered images. METHODS Based on the traits of parallel visual pathways, four types of facial expression images (happiness, fear, anger and neutral) with low, high and broadband spatial frequencies (LSF, HSF and BSF, respectively) were carefully created with the consideration of luminance, contrast and emotional intensity. These images were pseudo-randomly presented to 13 healthy subjects to record ERPs. Twenty recording electrodes were placed over the scalp according to the International 10-20 system. For emotion-relevant late negative components with latencies of 190-390 ms, the amplitude differences among the four facial expressions were analyzed for sequential 20-ms time windows by ANOVA. RESULTS There were significant amplitude differences between positive and negative LSF facial expressions in the early time windows of 270-310 ms at the occipitotemporal region. Subsequently, the amplitudes among negative HSF facial expressions differed significantly in the later time windows of 330-390 ms. CONCLUSIONS Discrimination between positive and negative facial expressions precedes discrimination among different negative expressions in a sequential manner based on parallel visual channels. SIGNIFICANCE ERPs with spatially filtered images have provided the first evidence for sequential discrimination of positive and negative facial expressions.

Differential roles of spatial frequency on reading processes for ideograms and phonograms: A high-density ERP study

The neural substrate of the dissociation between reading Japanese ideograms (Kanji) and phonograms (Kana) is currently unclear. To test whether spatial frequency (SF) information is responsible for this phenomenon, we recorded high-density event-related potentials (ERPs) with unfiltered or spatially filtered word stimuli in Japanese-speaking subjects. Kanji (early-learned, late-learned), Kana (word, non-word), and scrambled characters served as stimuli. Fourier analysis revealed that Kanji and Kana were characterized by high-SF (HSF) and low-SF (LSF) information, respectively. In ERPs with unfiltered stimuli, bilateral occipital P100, left occipitotemporal N170 and fronto-central N400 were elicited. Scrambled characters did not evoke left-lateralized N170 or clear N400. Under the LSF condition, P100 and N170 latencies for Kanji were significantly longer than those for Kana. In the HSF condition, P100 and N170 latencies for late-learned Kanji were significantly longer than those for early-learned Kanji. There was no significant difference in the N400 between Kanji and Kana in both SF conditions. These results suggest that early visual responses, but not the semantic component, are influenced by SF. This indicates a close link between Kana and LSF information, and between Kanji and HSF information. The differential effects of SF could underlie the neural basis of the differences between Kanji and Kana reading.

Neural responses in the occipital cortex to unrecognizable faces

OBJECTIVE Event-related potentials (ERPs) were recorded to examine neural responses to face stimuli in a masking paradigm. METHODS Images of faces (neutral or fearful) and objects were presented in subthreshold, threshold, and suprathreshold conditions (exposure durations of approximately 20, 30 and 300 ms, respectively), followed by a 1000-ms pattern mask. We recorded ERP responses at Oz, T5, T6, Cz and Pz. The effects of physical stimulus features were examined by inverted stimuli. RESULTS The occipital N1 amplitude (approximately 160 ms) was significantly smaller in response to faces than objects when presented at a subthreshold duration. In contrast, the occipitotemporal N170 amplitude was significantly greater in the threshold and suprathreshold conditions compared with the subthreshold condition for faces, but not for objects. The P1 amplitude (approximately 120 ms) elicited by upright faces in the subthreshold condition was significantly larger than for inverted faces. CONCLUSIONS P1 and N1 components at Oz were sensitive to subthreshold faces, which suggests the presence of fast face-specific process(es) prior to face-encoding. The N170 reflects the robustness of the face selective response in the occipitotemporal area. SIGNIFICANCE Even when presented for a subthreshold duration, faces were processed differently to images of objects at an early stage of visual processing.

The relationship between retrieval success and task performance during the recognition of meaningless shapes: An event-related near-infrared spectroscopy study

Retrieval success of episodic memory has been studied intensively through the investigation of old/new effects. Recognized stimuli used in event-related functional magnetic resonance imaging studies on old/new effects have been words and visual materials which can evoke semantic associations. To elucidate the neural basis of retrieval success uninfluenced by semantic processing, we investigated the correlation between old/new effects and task performance during the recognition of meaningless shapes, by using event-related near-infrared spectroscopy. Forty-two right-handed subjects made recognition judgments about old (studied) or new (unstudied) meaningless shapes. The old/new effects of the shapes were positively correlated with task performance in the bilateral inferior lateral parietal cortex (ILP), but predominantly in the left ILP. This finding indicated that the ILP was directly associated with retrieval success and its lateralization was consistently left-sided irrespective of the type of stimulus.

How Faces are Special: an ERP Study for Human Subliminal Face Processing

We demonstrate the perceptual specialization to faces that occurs at early visual stages, before conscious face recognition. Faces (neutral and fearful) or objects were briefly presented, followed by a 1000-ms mask stimulus. Event-related potentials (ERPs) in a subliminal presentation task were recorded at Oz, Cz, Pz, T5 and T6 (international 10-20 system). To determine the effect of subliminal face stimulation on ERPs, we firstly used subthreshold, threshold, and suprathreshold presentations with exposure durations of approximately 20, 30 and 300 ms respectively. Secondly, we adopted upright and inverted face presentations to examine whether ERPs elicited by subliminally presented faces resulted from face-specific brain responses rather than from the similarity of the physical features. The occipital P100 and N150 amplitudes for faces were significantly different from those for non-face stimuli in the subthreshold condition. Moreover, the occipital N150 amplitudes for the faces were significantly smaller than those for objects in the subthreshold condition. Conversely, there was no significant effect of subliminal stimulation with faces on the temporal N170 amplitude. However, the temporal N170 amplitudes for the faces, but not for the objects, increased in the threshold and suprathreshold conditions. Finally, the occipital P100 amplitude for inverted faces was significantly smaller than that for upright faces in the subthreshold condition. Furthermore, the face-specific response of the occipital N150 disappeared when inverted faces were presented. Our results suggest that output from the unconscious face processing route is integrated with conscious face processing activity, before the temporal face specific brain area perceives the necessary information.

P1-15 Face-sensitive neural responses in the occipital cortex without visual awareness

face of 18 persons (8 males and 10 females). Frontal and deviated faces were presented with a fixed gaze direction, followed by an apparent movement of eyes either toward the subject or away from the subject. Furthermore, eyes photographs with the apparent motion cut out from the face were also used as the stimulus. Subjects were eighteen student volunteers (8 males and 9 females). In ‘Direct gaze condition’, gaze direction moved toward the subject either from 30 degrees right or left location, and in ‘Averted gaze condition’, it moved away 30 degrees either right or left direction from the subject. EEG were recorded from Fz, Cz, Pz, C3, C4, T3, T4, T5 and T6 locations referred to nose-tip. The negative ERP component about 170 ms after stimulus onset (N170) were observed to the apparent movement of eyes both for face and eyes stimulus. This component was larger in ‘Direct gaze condition’ than in ‘Averted gaze condition’, suggesting that gaze contact relates to the specific processing different from averted gaze. Furthermore this N170 was interacted with the diretion of face.

58. Neural mechanisms of reading Japanese Kanji and Kana words: An fMRI study

abnormality; the age range of the subjects was 11–84 years (mean 51.6). The median, ulnar and tibial nerves were studied. Regression analysis was done to determine normal value. Results: The effect of age on FLM is relatively small, only 0.03– 0.05 ms/year. In contrast, FLM increases with height in arms by 0.12 (median) ms/cm or 0.13 (ulnar) ms/cm and in legs 0.22 (tibial) ms/cm. These effects are around half of the previous reports from Estonia (Puksa et al., 2003) or Brazil (Nobrega et al., 2004). From our database the upper limit of the normal value at 170 cm was 28 ms in median, 29 ms in ulnar and 51 ms in tibial nerve. Conclusion: FWML is highly correlated with height in Japanese. However, the effect is smaller than western people, reflecting the skeletal difference.

P36.12 Dual route model for recognition of faces and facial expressions: An event-related potential study with spatially filtered images

Background: The effects of the smell and taste stimulations are known from functional magnetic resonance imaging (fMRI) and electroencephalographic (EEG) studies. They have shown that the caudal orbitofrontal cortex, amygdala, insular cortex and anterior cingulate are activated by both modalities. Linear EEG investigations in time and frequency domain showed power and coherency changes in the alpha as well as theta bands depending on the quality of the stimulation. Only some analyses of non-linear nature were found. Aim/objective: Of the present study was to investigate the short term effects of an acute smell and taste stimulation in healthy adult volunteers by the PD2 analysis of Skinner and Molnar. Methods: Nine persons (seven females, two males) with an average age of 49 ± 19 years participated in the examination. Sixty seconds of 16 channel EEGs – according to 10/20 system – were recorded by an EEG 16X equipment and digitized by a LI-01/A interface (Mikromed) at a rate of 256 sample/s. After the first 30 s which was taken as a basal period for the comparison a fresh perfume cap or a piece of milk chocolate was presented. The period after the stimulation was divided in two 15 sec long parts and their PD2 results were compared to the basal condition by non-parametric signed rank test of Wilcoxon. Results: it was found that there was a significant decrease in the average of the PD2 after the olfactory stimulation on both sides. A short lasting about 15 s long decrease was found in the F3, O1 and C4 leads. Longer decreases have appeared in the F7, T4, P4 leads and the SD values decreased around the above mentioned positions. The effects after gustatory stimulation were less pronounced and late. Significant decrease of the average PD2 was found only in the right side, on the C4 and O2 leads. Conclusion: it is concluded that the PD2 analysis of the EEGs looks suitable for finding differences in the data processing after olfactory and gustatory stimulation.