The processing of non-symbolic numerical magnitudes as indexed by ERPs

Previous research has shown that, in the context of event-related potential (ERP) prime-target experiments, processing meaningful stimuli such as words, phonemes, numbers, pictures of objects, and faces elicit negativities around 400 ms. However, there is little information on whether non-symbolic numerical magnitudes elicit this negative component. The present experiments recorded ERPs while adults made same/different judgments to serially presented prime-target pairs of non-symbolic numerical stimuli containing the same, close, or distant quantities. In Experiment 1, a negativity between 350 and 450 ms was elicited for targets preceded by primes of unequal quantity, and this was greater for close than for distant quantities. Change direction (decreasing or increasing) also modulated a similar negativity: a greater negativity was elicited by targets preceded by larger than by smaller quantities. Experiment 2 replicated the numerical distance and change direction effects for numerical judgments, but found no negative distance effect in a color comparison task when the same stimuli were used. Additionally, ERP effects of numerical distance were found under implicit conditions, and task proficiency in the number condition modulated implicit and explicit numerical distance ERP effects. These results suggest that the neural systems involved with processing numerical magnitudes contribute to the construction of meaningful, contextual representations, are partly automatic, and display marked individual differences.     

Neural dynamics of attending and ignoring in human auditory cortex

Studies in all sensory modalities have demonstrated amplification of early brain responses to attended signals, but less is known about the processes by which listeners selectively ignore stimuli. Here we use MEG and a new paradigm to dissociate the effects of selectively attending, and ignoring in time. Two different tasks were performed successively on the same acoustic stimuli: triplets of tones (A, B, C) with noise-bursts interspersed between the triplets. In the COMPARE task subjects were instructed to respond when tones A and C were of same frequency. In the PASSIVE task they were instructed to respond as fast as possible to noise-bursts. COMPARE requires attending to A and C and actively ignoring tone B, but PASSIVE involves neither attending to nor ignoring the tones. The data were analyzed separately for frontal and auditory-cortical channels to independently address attentional effects on low-level sensory versus putative control processing. We observe the earliest attend/ignore effects as early as 100 ms post-stimulus onset in auditory cortex. These appear to be generated by modulation of exogenous (stimulus-driven) sensory evoked activity. Specifically related to ignoring, we demonstrate that active-ignoring-induced input inhibition involves early selection. We identified a sequence of early (<200 ms post-onset) auditory cortical effects, comprised of onset response attenuation and the emergence of an inhibitory response, and provide new, direct evidence that listeners actively ignoring a sound can reduce their stimulus related activity in auditory cortex by 100 ms after onset when this is required to execute specific behavioral objectives.     

Effects of symbol type and numerical distance on the human event-related potential

This study investigated the influence of the symbol type and numerical distance of numbers on the amplitudes and peak latencies of event-related potentials (ERPs). Our aim was to (1) determine the point in time of magnitude information access in visual number processing; and (2) identify at what stage the advantage of Arabic digits over Chinese verbal numbers occur. ERPs were recorded from 64 scalp sites while subjects (n = 26) performed a classification task. Results showed that larger ERP amplitudes were elicited by numbers with distance-close condition in comparison to distance-far condition in the VPP component over centro-frontal sites. Furthermore, the VPP latency varied as a function of the symbol type, but the N170 did not. Such results demonstrate that magnitude information access takes place as early as 150 ms after onset of visual number stimuli and the advantage of Arabic digits over verbal numbers should be localized to the VPP component. We establish the VPP component as a critical ERP component to report in studies of numerical cognition and our results call into question the N170/VPP association hypothesis and the serial-stage model of visual number comparison processing.     

Audiovisual temporal discrimination is less efficient with aging: an event-related potential study

We investigated the crossmodal temporal discrimination deficit characterizing older adults and its event-related potential (electroencephalogram) correlates using an audiovisual temporal order judgment task. Audiovisual stimuli were presented at stimulus onset asynchronies (SOA) of 70 or 270 ms. Older were less accurate than younger adults with an SOA of 270 ms but not 70 ms. With an SOA of 270 ms only, older adults had smaller posterior P1 and frontocentral N1 amplitudes for visual stimuli in auditory-visual trials and auditory stimuli in visual-auditory trials, respectively. These results suggest a deficit in cross-sensory processing with aging reflected at the behavioural and neural level, and suggest an impairment in switching between modalities even when the inputs are separated by long temporal intervals.     

Cat's behavioral sensitivity and cortical spatiotemporal responses to the sweep direction of frequency-modulated tones

Neural responses to frequency modulated (FM) sweeps have been well investigated in single-units using electrophysiological recording methods. However, rare psychophysical experiments were conducted to investigate behavioral discrimination of FM-sweeps in the same species used in physiological experiments. Also, the previous studies have not focused on how the population of cortical neurons works together to encode the direction of FM-sweeps. To investigate the relation between the behavioral perception of FM direction and the population coding, we examined the cat's capability to discriminate the upward and downward FM-sweeps and recorded the neural responses to the same stimuli from the primary auditory cortex (A1) in different awake cats. We found that cats showed high performance to detect the change of direction of FM-sweeps, which linearly swept between 0.1 and 16kHz in 40-160ms duration; however, the behavioral performance obviously deteriorated when the sweeps were shortened to 10-20ms. Physiological results indicated that the upward sweeps elicited a temporal sequence of responses among the A1 neurons, in which neurons tuning to low-frequencies responded earlier and those tuning to high-frequencies later, while the response sequence was reversed when A1 was driven by the downward sweeps. The rank-order of response latencies could provide a reliable discrimination of the FM direction, and the discrimination performance paralleled with the cat's behavioral performance. Our result suggests that the relative response timings in A1 contain enough information used by subsequent processing stages to make the decision of FM direction.     

Transient interference of right hemispheric function due to automatic emotional processing

We examined the effects of emotional stimuli on right and left hemisphere detection performance in a hemifield visual discrimination task. A group of 18 healthy subjects were asked to discriminate between upright and inverted triangles (target). Targets were randomly presented in the left or right visual hemifield (150 ms target duration). A brief emotional picture (pleasant or unpleasant; 150 ms stimulus duration) or neutral picture selected from the International Affective Picture System was randomly presented either in the same (47%) or the opposite (47%) spatial location to the subsequent target. Emotional or neutral stimuli offset 150 ms prior to the subsequent target. Subjects were instructed to ignore the pictures and respond to the targets as quickly and accurately as possible. Independent of field of presentation, emotional stimuli prolonged reaction times (P < 0.01) to LVF targets, with unpleasant stimuli showing a greater effect than pleasant stimuli. The current study shows that brief emotional stimuli selectively impair right hemispheric visual discrimination capacity. The findings suggest automatic processing of emotional stimuli captures right hemispheric processing resources and transiently interferes with other right hemispheric functions.     

N4 component responses to pre-pulse startle stimuli in young adults: relationship to alcohol dependence

Both physiological and behavioral studies provide evidence to suggest that deficits in frontal cortical control circuits may contribute to the risk for developing alcohol dependence. Event-related potential (ERP) and eye blink responses to startle and short delay prepulse-plus-startle stimuli, and psychiatric diagnoses were investigated in young adult (age 18-30 years) men (n = 135) and women (n = 205) Mexican Americans. Women displayed a significant increase in the amplitude of the eye blink response to both the startle and pre-pulse-plus-startle stimuli. None of the psychiatric diagnoses were associated with differences in eye blink responses. ERP responses to the startle and prepulse-plus startle stimuli included a negative polarity wave at approximately 400 ms that was of the highest amplitude in the frontal leads (N4S). Women were found to have significantly higher amplitude N4S responses than men. Participants with alcohol dependence demonstrated significantly less inhibition and more facilitation of the N4S component by the pre-pulse stimuli. This finding was not associated with a diagnosis of: any other drug dependence disorder (including nicotine), anxiety or affective disorder, or conduct/antisocial personality disorder. The present study suggests that gender and a lifetime diagnosis of alcohol dependence may selectively contribute to this frontal late wave electrophysiological response to prepulse-plus-startle stimuli.     

The role of the right parietal cortex in sound localization: a chronometric single pulse transcranial magnetic stimulation study

Auditory spatial functions, including the ability to discriminate between the positions of nearby sound sources, are subserved by a large temporo-parieto-frontal network. With the aim of determining whether and when the parietal contribution is critical for auditory spatial discrimination, we applied single pulse transcranial magnetic stimulation on the right parietal cortex 20, 80, 90 and 150 ms post-stimulus onset while participants completed a two-alternative forced choice auditory spatial discrimination task in the left or right hemispace. Our results reveal that transient TMS disruption of right parietal activity impairs spatial discrimination when applied at 20 ms post-stimulus onset for sounds presented in the left (controlateral) hemispace and at 80 ms for sounds presented in the right hemispace. We interpret our finding in terms of a critical role for controlateral temporo-parietal cortices over initial stages of the building-up of auditory spatial representation and for a right hemispheric specialization in integrating the whole auditory space over subsequent, higher-order processing stages.     

Learning and integration of rewarding and aversive stimuli in the rat lateral hypothalamus

Single neuron activity was recorded in the lateral hypothalamus (LHA) and lateral preoptic-anterior hypothalamic area (IPOA-AHA) of the rat during discrimination learning of cue tones that predicted glucose or intracranial self-stimulation as rewarding stimuli, or electric shock or tail pinch as aversive stimuli, using identical behavior, licking. Rewarding and aversive stimuli had opposite effects on the same LHA neurons, but had the same effects on IPOA-AHA neurons. Neurons in the LHA that differentiated between reward and aversion acquired discrimination of the respective cue tones, while IPOA-AHA neurons responded in the same way to cue tones whether they preceded reward or aversion. The results suggest reward- and aversion-related integrative functions in the LHA and arousal or attentional functions in the IPOA-AHA.     

The mismatch negativity as an index of temporal processing in audition

Objectives: The relation of the mismatch negativity (MMN) elicitation with behavioral stimulus discrimination as well as the replicability of the MMN was evaluated for intervals between paired tones.Methods: The MMN, obtained in a passive oddball paradigm in two sessions separated by 4–21 days and behavioral responses (button presses to target stimuli) in a separate session were recorded from 10 adult healthy subjects. The standard stimulus (P=0.79) was a tone pair separated by a 120 ms silent inter-stimulus interval (ISI) and the deviant stimuli were tone pairs with an ISI of 100, 60, and 20 ms (P=0.07 for each).Results: The 20 and 60 ms ISI deviant tone pairs elicited a significant MMN during both recording sessions and they were also behaviorally discriminated, whereas neither did the 100 ms ISI deviant pair elicit significant MMN nor was it behaviorally discriminated. Furthermore, there was a significant correlation between the MMN and reaction times to the 20 and 60 ms ISI deviant pairs. The 20 ms ISI deviant stimulus elicited highly replicable MMNs (r=0.75), whereas the less well discriminated 60 ms ISI deviant pair did not (r=0.60).Conclusions: The MMN reflects discrimination accuracy of temporal sound intervals. Furthermore, when the physical difference between the standard and deviant tone pair in the temporal domain is large, it is elicited with high reliability.     

250 ms to code for action affordance during observation of manipulable objects

It is well known that viewing graspable tools (but not other objects) activates motor-related brain regions, but the time course of affordance processing has remained relatively unexplored. In this study, EEG was continuously recorded from 128 scalp sites in 15 right-handed university students while they received stimuli in the form of 150 pictures of familiar non-tool objects and 150 pictures of manipulable tools, matched for size, luminance and perceptual familiarity. To select the 300 images for the study, a wider set of preliminary stimuli was screened for motoric content by 20 judges using a 3-point scale (0 = absent; 2 = strong); pictures that scored below 1.5 or above 0.6 were excluded from the tool and non-tool categories, respectively. Tools and non-tools were presented in random order, interspersed with 25 photos of live plants. Each slide was presented for 1000 ms, with an interval ranging from 1500 to 1900 ms. The task consisted of responding to the photos of plants while ignoring the other stimuli. Both an anterior negativity (210-270 ms) and a centroparietal P300 (550-600 ms) were larger in response to tools than objects, particularly in the left hemisphere. swLORETA inverse solution identified the occipito-temporal cortex (BA19 and BA37) as the most significant source of activity (in the 210-270-ms time window) for both types of visual objects and the left postcentral gyrus (BA3) and the left and right premotor cortex (BA6) as the most significant source of activity for tools only. These data hint at an automatic access to motoric object properties even under conditions in which attention is devoted to other stimulus categories.     

Neurophysiological correlates of face gender processing in humans

Event-related potentials (ERPs) were recorded while subjects were involved in three gender-processing tasks based on human faces and on human hands. In one condition all stimuli were only of one gender, preventing any gender discrimination. In a second condition, faces (or hands) of men and women were intermixed but the gender was irrelevant for the subject's task; hence gender discrimination was assumed to be incidental. In the third condition, the task required explicit gender discrimination; gender processing was therefore assumed to be intentional. Gender processing had no effect on the occipito-temporal negative potential at approximately 170 ms after stimulation (N170 component of the ERP), suggesting that the neural mechanisms involved in the structural encoding of faces are different from those involved in the extraction of gender-related facial features. In contrast, incidental and intentional processing of face (but not hand) gender affected the ERPs between 145 and 185 ms from stimulus onset at more anterior scalp locations. This effect was interpreted as evidence for the direct visual processing of faces as described in Bruce and Young's model [Bruce, V. & Young, A. (1986) Br. J. Psychol., 77, 305-327]. Additional gender discrimination effects were observed for both faces and hands at mid-parietal sites around 45-85 ms latency, in the incidental task only. This difference was tentatively assumed to reflect an early mechanism of coarse visual categorization. Finally, intentional (but not incidental) gender processing affected the ERPs during a later epoch starting from approximately 200 ms and ending at approximately 250 ms for faces, and approximately 350 ms for hands. This later effect might be related to attention-based gender categorization or to a more general categorization activity.     

Associative learning in humans--conditioning of sensory-evoked brain activity

A classical conditioning paradigm was employed in two experiments performed on 35 human volunteers. In nine subjects, the presentation of Landolt rings (conditioned stimuli, CS + ) was paired with an electric stimulus (unconditioned stimuli, UCS) applied to the left median nerve. Neutral visual control stimuli were full circles (CS -) that were not paired with the UCS. The skin conductance response (SCR) was determined in a time interval of 5 s after onset of the visual stimuli, and it was measured in the acquisition and test phase. Associative learning was reflected by a SCR occurring selectively with CS +. The same experiment was repeated with another group of 26 adults while electroencephalogram (EEG) was recorded from 30 electrodes. For each subject, mean evoked potentials were computed. In 13 of the subjects, a conditioning paradigm was followed while the other subjects served as the control group (non-contingent stimulation). There were somatosensory and visual brain activity evoked by the stimuli. Conditioned components were identified by computing cross-correlation between evoked somatosensory components and the averaged EEG. In the visual evoked brain activity, three components with mean latencies of 105.4, 183.2, and 360.3 ms were analyzed. Somatosensory stimuli were followed by major components that occurred at mean latencies of 48.8, 132.5, 219.7, 294.8, and 374.2 ms latency after the shock. All components were analyzed in terms of latency, field strength, and topographic characteristics, and were compared between groups and experimental conditions. Both visual and somatosensory brain activity was significantly affected by classical conditioning. Our data illustrate how associative learning affects the topography of brain electrical activity elicited by presentation of conditioned visual stimuli.     

Recognition advantage of happy faces: Tracing the neurocognitive processes

The present study aimed to identify the brain processes—and their time course—underlying the typical behavioral recognition advantage of happy facial expressions. To this end, we recorded EEG activity during an expression categorization task for happy, angry, fearful, sad, and neutral faces, and the correlation between event-related-potential (ERP) patterns and recognition performance was assessed. N170 (150–180 ms) was enhanced for angry, fearful and sad faces; N2 was reduced and early posterior negativity (EPN; both, 200–320 ms) was enhanced for happy and angry faces; P3b (350–450 ms) was reduced for happy and neutral faces; and slow positive wave (SPW; 700–800 ms) was reduced for happy faces. This reveals (a) an early processing (N170) of negative affective valence (i.e., angry, fearful, and sad), (b) discrimination (N2 and EPN) of affective intensity or arousal (i.e., angry and happy), and (c) facilitated categorization (P3b) and decision (SPW) due to expressive distinctiveness (i.e., happy). In addition, N2, EPN, P3b, and SPW were related to categorization accuracy and speed. This suggests that conscious expression recognition and the typical happy face advantage depend on encoding of expressive intensity and, especially, on later response selection, rather than on the early processing of affective valence.     

Neural substrates of visual perceptual learning of simple and complex stimuli.

OBJECTIVE: The two experiments described here used event-related potentials (ERPs) to investigate whether perceptual learning of different complexities of stimuli involves different levels of visual cortical processing in human adults. METHODS: Reaction times and ERPs were recorded during 3 consecutive training sessions in which subjects discriminated between simple stimuli made of line segments or complex stimuli made of compound shapes. RESULTS: Reaction times in both experiments were shortened across training sessions. For simple stimuli, training resulted in a decreased N1 (125-155ms) and an increased P2 (180-240ms) over the occipital area. For complex stimuli, however, training resulted in a decreased N1 (125-155ms) and N2 (290-340ms) and an increased P3 (350-550ms) over the central/parietal areas. CONCLUSIONS: These findings suggest that perceptual learning modifies the response at different levels of visual cortical processing related to the complexity of the stimulus. SIGNIFICANCE: The neuronal mechanisms involved in perceptual learning may depend on the nature (e.g. the complexity) of the stimuli used in the discrimination task.     

Activity of neurons in monkey posterior temporal cortex during multidimensional visual discrimination tasks

Unit activity was recorded from the posterior temporal cortex (PTE) of awake, behaving rhesus monkeys while they performed a series of visual discrimination tasks involving colored checkerboard patterns. The activity of 130 (91%) of 143 PTE units was altered by the presentation of a visual discriminandum; 112 of these cells (86%) exhibited a significant increase in firing after presentation of the stimulus while the remainder gave an inhibitory response. Over half (64%) the PTE units exhibited differential activity between discriminanda, i.e. they were selective for color and/or form. Six of 10 neurons, recorded when the monkey was required to shift attention from one stimulus feature to another, exhibited a difference in poststimulus neural activity even though the discriminandum remained the same. Three neurons were recorded from when the stimuli were altered by changing the check size although the relevant (i.e. rewarded) dimension (color) was left the same; two showed an invariant response to the altered stimuli and one gave the same response to one of the altered stimuli but a different response to the other. These data support the role of posterior temporal cortex in visual discrimination learning and visual attention.     

Interstimulus interval effect on event-related potential N270 in a color matching task.

Event-related brain potentials were recorded in a matching task, in which subjects were asked to discriminate if the color of the second stimulus (S2) was the same as the first stimulus (S1). The interstimulus interval between the two stimuli of a pair was of three levels (150 ms, 500 ms and 1000 ms). A negative component about 270 ms after the presentation of S2 was elicited when the color of the two stimuli was not identical for the interstimulus interval of 500 ms and 1000 ms, but not for the interval of 150 ms. This may suggest that N270 represented the response of the brain to conflicting information between different cortical levels.     

Tactile body image disturbance in anorexia nervosa

Body image disturbances are central to anorexia nervosa (AN). Previous studies have focused mainly on attitudinal and visual aspects. Studies on somatosensory aspects thus far have been scarce. We therefore investigated whether AN patients and controls differed in tactile perception, and how this tactile body image related to visual body image and body dissatisfaction. The Tactile Estimation Task (TET) measured tactile body image: Two tactile stimuli were applied to forearm and abdomen, and, while blindfolded, participants estimated the distance between the two tactile stimuli between their thumb and index finger. The Distance Comparison Task (DCT) measured visual body image. Compared to controls (n = 25), AN patients (n = 20) not only visualized their body less accurately, but also overestimated distances between tactile stimuli on both the arm and abdomen, which might reflect a disturbance in both visual and tactile body image. High levels of body dissatisfaction were related to more severe inaccuracies in the visual mental image of the body, and overestimation of tactile distances. Our results imply that body image disturbances in AN are more widespread than previously assumed as they not only affect visual mental imagery, but also extend to disturbances in somatosensory aspects of body image.     

Maturation of cortical mismatch responses to occasional pitch change in early infancy: effects of presentation rate and magnitude of change

Previous studies have reported two types of event-related potential (ERP) mismatch responses in infants to infrequent auditory changes: a broad discriminative positivity in younger infants and a negativity resembling adult mismatch negativity (MMN) in older infants. In the present study, we investigated whether the positive discriminative slow wave and the adult-like MMN are functionally distinct by examining how they are affected by presentation rate and magnitude of change. We measured ERPs from adults, 2-month-olds, and 4-month-olds to a repeating piano tone (standard) that occasionally changed in pitch (deviant). The pitch changes between standards and deviants were either small (1/12 octave) or large (1/2 octave) in magnitude, and the stimulus presentation rate was either slow (800 ms SOA) or fast (400 ms SOA). As the presentation rate increased, both adults and 4-month-olds showed an MMN response that decreased in latency, but was unaffected in amplitude. As the magnitude of the pitch change increased, MMN increased in amplitude. On the other hand, only a broad positive mismatch response was seen in 2-month-olds. As the presentation rate increased, 2-month-olds’ responses to standard tones decreased in amplitude while their responses to deviant tones were unaffected. The magnitude of the pitch change did not affect 2-month-olds’ responses. These results suggest that pitch is processed differently in auditory cortex by 2-month-olds and 4-month-olds, and that a cortical change-detection mechanism for pitch discrimination similar to that of adults emerges between 2 and 4 months of age.     

Mismatch responses related to temporal discrimination of somatosensory stimulation.

OBJECTIVE: To determine the existence of a pre-attentively evoked somatosensory mismatch negativity component and to investigate the use of that component in objective clinical diagnostics. METHODS: First we determined the temporal discrimination threshold (DT) of paired stimuli in each subject, and applied two sequential electrical stimuli to the hand with paired stimulus times of (1) DT-10 ms, (2) DT-30 ms and (3) DT+50 ms. Then, we recorded ERPs using an oddball paradigm, frequent (standard) and rare (deviant). We used two stimuli, DT-30 ms and DT-10 ms, in the first experiment, and DT-30 ms and DT+50 ms, in the second experiment. RESULTS: In each experiment, two specific components, a negative component peaking at approximately 60ms (N60) and a large positive component peaking around 100-200 ms (P150), were identified, mainly following the deviant stimulus, which were considered somatosensory mismatch components. N60 was more remarkably identified in the second experiment and P150 in the first. CONCLUSIONS: N60 might be generated during tasks which subjects can clearly discriminate, but P150, which seems to correspond to auditory mismatch negativity, might be generated in tasks which require fine discrimination. SIGNIFICANCE: We confirmed that our new method could be used for the objective examination of temporal discrimination.