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The auditory mismatch negativity, a component of the event-related potential elicited by an unexpected stimulus in a sequence of acoustic stimuli, provides an objective measure of the accuracy of the echoic information processing of the human brain in vivo. Auditory mismatch negativity is also a useful probe of cortical glutamatergic N-methyl-d-aspartate receptor activity and disturbance. Notably, auditory mismatch negativity is consistently impaired in schizophrenia. Because of the wide spectrum extending from bipolar affective illness and schizoaffective psychosis to typical schizophrenia, we examined the literature on auditory mismatch negativity in bipolar disorder with the aim to find any neurophysiological dysfunction concerning pre-attentive information processing shared by these clinical conditions. This focused review includes 26 original articles published in peer-reviewed journals and indexed in the National Institutes of Health National Library of Medicine (PubMed) search system. Overall, evidence is consistent with the finding that auditory mismatch negativity is impaired in bipolar disorder with psychotic features, even though to a lesser extent than in schizophrenia. It must be acknowledged that, in a few twin and family studies, mismatch negativity abnormalities were not specifically associated with bipolar disorder. In conclusion, auditory mismatch negativity research supports the involvement of the N-methyl-d-aspartate system in the pathophysiology of bipolar disorder, as previously assessed for schizophrenia, thus creating an intriguing trait d’union between these two mental illnesses and stimulating the development of novel therapeutic agents. With additional replication and validation, auditory mismatch negativity may be further considered as a correlate of a common psychopathology of schizophrenia and bipolar spectrum illnesses.

According to the cognitive processing perspectives, patients with insomnia have insufficient neural management of expressional information. In this study, we compared the pre-attentive processing function of task-irrelevant facial expressions in patients with primary insomnia (PI) and matched healthy controls, with expression-related mismatch negativity (EMMN) elicited by emotional faces as the indicator. Using three schematic facial expressions (neutral, happy, and sad) as task-irrelevant stimuli, we investigated the visual processing of PI patients (n = 22) and healthy subjects (n = 22) in an expression-related oddball paradigm designed to elicit the visual N170 and EMMN component. After recording and analyzing the electroencephalogram of all participants, amplitude analysis of N170 and EMMN was eventually conducted under corresponding time window. Compared with control group, the amplitude of sad-EMMN component was significantly attenuated in patients with PI, while no remarkable difference was observed under the happy condition. In addition, negative cognitive bias was further validated in the control group, but not presented in the PI group. The current data suggest dysfunctional expressional information processing in PI patients, accompanied by the disorganization of high level perceptual strategy of processing facial emotional expression.

Defensive reactions need to be quick and appropriate to ensure survival. So, it is crucial that threats trigger immediate action upon detection, even in the absence of awareness. Also, the form of such action should be appropriate to the imminence of the threat. Thus, attention should be guided by signals of increasing threat imminence. We examined whether subliminally presented threat stimuli provoke automatic avoidance tendencies and whether threat cues’ distance change and threat potential determine attention allocation. Following fear conditioning, participants performed an approach-avoidance task with subliminally presented conditioned threat and safety stimuli and an attentional bias task with approaching versus distancing signals of threat and safety. Pre-attentive processing of threat cues resulted in approach rather than avoidance tendencies; attention was captured preferentially by signals of increasing threat imminence. The results support the importance of threat imminence and extend findings of previous research on pre-attentive influences on defensive responding. ispartof: Emotion vol:17 issue:2 pages:251-258 ispartof: location:United States status: published

The neutral tone is a unique tone form in Mandarin as it distinguishes from four canonical tones or full tones on the one hand and integrates phonetic, morphological, syntactical and prosodic information on the other hand. Research to date has been focusing on its unique and variant acoustic features. However, little is known about how native Mandarin speakers process such a unique tone. In the present study, the mismatch negativity was used to explore the comparison-based pre-attentive change detection of Mandarin neutral tone. The mismatch negativity at the time window of 400-800 ms post-first-tone onset was obtained by subtracting event-related potentials to standard neutral tone from event-related potentials to a deviant natural tone. The source analysis of mismatch negativity showed the cortex generator was located at the left temporal lobe. The data suggest that Chinese native speakers process neutral tone automatically under non-attentional conditions, as revealed by the mismatch negativity data aligned with a neutral tone, and that neutral tone does exist as an automatically recognizable one in native Mandarin speakers’ tone system.

Negative bias in cognition is closely associated with susceptibility to recurrent episodes of depression. Given the high recurrence rate of depression, previous studies have focused on the attentive level in late-life depression (LLD), but depression relapse is difficult to detect as a lower chief complaint in elderly people. Facial expression mismatch negativity (EMMN) is a tool that can measure cognitive bias in pre-attentive processing. In this study, we sought to explore the cognitive bias in pre-attentive emotional information processing in LLD. Thirty patients with remitted LLD and 30 non-depressed, age- and gender-matched normal controls (NC) were enrolled in this study. Automatic emotional processing was elicited by using an expression-related oddball paradigm in all participants. There were no significant differences in N170 amplitude and latency between remitted LLD and NC. Compared with NC subjects, patients with remitted LLD demonstrated an attenuated mean amplitude of positive and negative EMMN, whereas the mean amplitude of negative EMMN in remitted LLD was much larger than that of positive EMMN. Our findings suggest that although basic processing of facial expressions is intact in remitted LLD, automatic processing of facial expressions in remitted LLD is impaired with a negative bias in cognition. Further investigation of the contributions of negative bias in EMMN to susceptibility to recurrence of LLD is warranted.

Depression is associated with bias in emotional information processing, but less is known about the processing of neutral sensory stimuli. Of particular interest is processing of sound intensity which is suggested to indicate central serotonergic function. We tested weather event-related brain potentials (ERPs) to occasional changes in sound intensity can dissociate first-episode depressed, recurrent depressed and healthy control participants. The first-episode depressed showed larger N1 amplitude to deviant sounds compared to recurrent depression group and control participants. In addition, both depression groups, but not the control group, showed larger N1 amplitude to deviant than standard sounds. Whether these manifestations of sensory over-excitability in depression are directly related to the serotonergic neurotransmission requires further research. The method based on ERPs to sound intensity change is fast and low-cost way to objectively measure brain activation and holds promise as a future diagnostic tool. acceptedVersion

This study investigated the effect of hyperthermia on pre-attentive processing by recording the mismatch negativity (MMN) component of ERPs. 36 right-handed young male undergraduates were divided into two groups, a control group with 1h of exposure at 25°C and a heat group with 1h of exposure at 50°C. MMNs were recorded before and after heat exposure. It was found that, although there was no group difference before heat exposure, MMN declined significantly in the heat group compared to the control group after heat exposure for 1h, indicating that passive heat exposure could damage pre-attentive processing. The MMN component could be a good index to assess cognitive functioning in a hot environment.

The pre-attentive processing of Cantonese tones was studied with an auditory passive oddball paradigm. Event-related potentials to standard and deviant auditory stimuli were recorded as participants watched a silent movie attentively. The standards and deviants differed in either pitch level or pitch contour. Mismatch negativity (MMN) and P3a were elicited by all types of deviant tones, suggesting that lexical tone was processed pre-attentively. In addition, the size and latency of MMN were sensitive to the size of pitch level change, while the latency of P3a captured the presence of pitch contour change. These results indicate that pitch contour and pitch height are two important dimensions in sensory processing of lexical tones.

Objective: To determine whether people with dementia (PwD), and carers of PwD, show a processing bias\ud to dementia-related words in an emotional Stroop task, and if so, whether the presence of such a bias is\ud related to level of explicit awareness of the condition.\ud \ud Method: Seventy-nine people with early stage Alzheimer’s disease (AD), vascular or mixed dementia, and\ud their carers, completed an emotional Stroop task. Time taken to colour-name dementia-related and\ud neutral words was compared within and between groups. Additionally, as a comparison, ratings of the\ud awareness of the condition shown by PwD were made on the basis of a detailed interview with each PwD\ud and his/her carer.\ud \ud Results: PwD and carers showed the same level of increase in response times to salient compared to\ud neutral words. In the PwD this effect was unrelated to the degree of awareness that they demonstrated\ud regarding the condition.\ud \ud Conclusions: The emotional Stroop effect in response to dementia-related words in PwD indicates that\ud preserved implicit awareness of the condition can be elicited even where there is reduced explicit\ud awareness.

Background Deficits of pre-attentive information processing have been frequently found in patients with major depressive disorder, nevertheless the results are quite inconsistent due to clinical heterogeneity and methodological difference. Cognitive processing of music is a useful tool for investigating human cognition and its underlying brain mechanisms. Although general auditory processing and perception of musical sound are hampered in patients with MDD, whether the deficits in musical processing begin from pre-attentive stage is not well investigated yet. The present study aimed to investigate the MMN of musical sound in patients with MDD. Method MMN responses to different musical features were compared in 20 patients with MDD and 20 age-matched healthy controls. The multi-feature paradigm was used to examine automatic change detection of six different musical sound features (pitch, timbre, location, intensity, slide, rhythm) in a complex musical context. Severity of depression and co-morbid anxiety were evaluated using the Hamilton Rating Scale of Depression (HRSD-17) and the Hamilton Anxiety Rating Scale (HAMA). Results MMNs were obtained with all deviants. The timbre-MMN was significantly larger in MDD patients than in healthy controls, while the other deviants (pitch, location, intensity, slide and rhythm) elicited similar MMN across groups. For MDD patients, the amplitudes and latencies of MMNs did not correlate with severity of depression or co-morbid anxiety. Limitations The sample size in this study is relatively small. Conclusion Patients with MDD do not perform at the same level as controls in automatic change detection of timbre. This dysfunction is considered to be a trait-dependent feature of MDD.

The purpose of the present study was to examine the role of trait anxiety and social desirability on skin conductance responses (SCRs) following exposure to masked and unmasked pictures in a non-clinical sample. The most prominent results were found with regard to masked pictures (i.e. subliminal). Higher levels of social desirability were associated with a decrease in SCRs to masked threat pictures (relative to neutral), whereas elevated levels of trait anxiety were associated with an increase in SCRs. This latter effect, however, was mainly seen among participants who simultaneously scored low on social desirability. These results were discussed in terms of trait anxiety (combined with lower social desirability scores) being associated with (i) enhanced autonomic responses to threatening information most evident at a pre-attentive level, that (ii) may potentially be a vulnerability marker for anxiety disturbances.

The present study was designed to test the hypothesis of unconscious attending to alcohol-related information in alcoholics experiencing a high level of craving for alcohol. Subjects included a group of alcoholics ( n =34) divided by a median split on a craving measure into two groups labeled as ‘high craving’ ( n =18) and ‘low craving’ ( n =16) alcoholics, and a non-alcoholic control group ( n =39). The cardiovascular reactions of these groups were compared after their exposure to masked and unmasked alcohol and control stimuli. As expected the ‘high craving’ alcoholics showed an immediate heart rate deceleration after exposure to masked and non-consciously accessible alcohol pictures. The ‘high craving’ alcoholics reported a small but significant increase in difficulty resisting a drink after exposure to masked alcohol pictures. When the alcohol pictures were presented unmasked a significant increase was found in both high and low craving alcoholics on consciously expressed urges, fidgeting and reduced coping with temptation to drink. The ‘high craving’ alcoholics had lower tonic heart rate variability compared to the control group and the level of craving was positively associated with salivation during the exposure to all picture types. The findings generally support the psychobiological theory of craving, which suggests that the uncontrollability of the craving experience is rooted in unconscious processing of drug-related information.

It has been hypothesized that auditory temporal processing plays a major role in the aetiology of dyslexia. Event-related brain potentials (mismatch negativity, MMN) of auditory temporal processing were assessed in 15 dyslectic adults and 20 controls. A complex tonal pattern was used where the difference between standard and deviant stimuli was the temporal, not the frequency structure. Dyslexics had a significantly smaller MMN in the time window of 225-600 ms. This result shows that dyslexics have a significant pre-attentive deficit in processing of rapid temporal patterns suggesting that it may be the temporal information embedded in speech sounds, rather than phonetic information per se, that resulted in the attenuated MMN found in dyslexics in previous studies. MMN scalp topographies were similar for both groups, showing a maximum over fronto-central leads.

The purpose of this study was to test the previous report that generation of the mismatch negativity (MMN) component of event-related brain potentials (ERPs) is indifferent to the predictable occurrence of stimulus deviance. A pattern of standards (S) and deviants (D) were delivered in a predictable fashion (SSSSD) at two different speeds (1.3 s and 100 ms). An MMN was obtained to the D position tone at the slow but not the fast pace. These results demonstrate that, unlike the P3 component, the MMN is sensitive to the predictable occurrence of stimulus deviance when the predictability can be detected by the brain within the estimated limits of sensory memory.

Neuronal mechanisms involved in the processing of complex sounds with asynchronous onsets were studied in reading subjects. The sound onset asynchrony (SOA) between the leading partial and the remaining complex tone was varied between 0 and 360 ms. Infrequently occurring deviant sounds (in which one out of 10 harmonics was different in pitch relative to the frequently occurring standard sound) elicited the mismatch negativity (MMN), a change-specific cortical event-related potential (ERP) component. This indicates that the pitch of standard stimuli had been pre-attentively coded by sensory-memory traces. Moreover, when the complex-tone onset fell within temporal integration window initiated by the leading-partial onset, the deviants elicited the N2b component. This indexes that involuntary attention switch towards the sound change occurred. In summary, the present results support the existence of pre-perceptual integration mechanism of 100-200 ms duration and emphasize its importance in switching attention towards the stimulus change.

Objective Despite ongoing debate about gender differences in pre-attention processes, little is known about gender effects on change detection for auditory and visual stimuli. We explored gender differences in change detection while processing duration information in auditory and visual modalities. Method We investigated pre-attentive processing of duration information using a deviant-standard reverse oddball paradigm (50ms/150ms) for auditory and visual mismatch negativity (aMMN and vMMN) in males and females ( n =21/group). Result In the auditory modality, decrement and increment aMMN were observed at 150–250ms after the stimulus onset, and there was no significant gender effect on MMN amplitudes in temporal or fronto-central areas. In contrast, in the visual modality, only increment vMMN was observed at 180–260ms after the onset of stimulus, and it was higher in males than in females. Conclusion No gender effect was found in change detection for auditory stimuli, but change detection was facilitated for visual stimuli in males. Significance Gender effects should be considered in clinical studies of pre-attention for visual stimuli.

Individuals frequently experience mental fatigue during or after prolonged periods of cognitive activity. We investigated the effects of mental fatigue on the ability to detect minor changes in the pre-attentive stage of information processing by recoding MMN of ERP components. The equal probable paradigm was employed to elicit pure memory-comparison-based MMN component. Mental fatigue was induced by the continuous performance for 2h of mental arithmetic tasks. MMN amplitudes at fronto-central electrode sites were significantly decreased in subjects with mental fatigue than in subjects under control conditions, whereas temporal MMN was not affected by mental fatigue. These results suggest that mental fatigue impairs pre-attentive processing.

RATIONALE: Studies have shown that alcohol could impair automatic pre-attentive change detection. However, several earlier studies which investigated alcohol-induced effects on single auditory feature independently were different from each other on the results. Meanwhile, only few auditory features have been investigated yet. Therefore, it is meaningful to investigate effects of alcohol on multiple auditory features in one experiment.OBJECTIVES: This study investigates the effects of alcohol on automatic pre-attentive change detection of four kinds of auditory features (frequency, intensity, location, and duration) in one experiment.METHODS: This study, using multi-feature oddball paradigm, compares and analyzes mismatch negativity (MMN) elicited by four kinds of auditory features (frequency, intensity, location, and duration), of 12 participants, under alcohol (0.65 g/kg) and non-alcohol condition.RESULTS: Compared to non-alcohol condition, amplitudes of all the four MMN types significantly declined under alcohol condition, and their amplitude decline ratios decreased as deviant magnitude became larger. Latencies of frequency and intensity MMN were delayed while latencies of location and duration MMN were not delayed significantly.CONCLUSION: Alcohol impaired automatic pre-attentive change detection of all the four auditory features (frequency, intensity, location, and duration). However, the alcohol-induced impairment magnitude on automatic pre-attentive detection of the four auditory features was different from each other. According to analysis of amplitude, frequency seems to be affected most among the four auditory features. According to analysis of latency, only frequency and intensity were affected.

Sixty-four children, aged 7 to 14 years, with early-treated PKU, were compared with control children on visual evoked potential (VEP) amplitudes and latencies and auditory mismatch negativity (MMN) amplitudes. It was further investigated whether indices of dietary control would be associated with these evoked potentials parameters. There were no significant differences between controls and children with PKU in VEP- and MMN-indices. However, higher lifetime Phe levels were, in varying degree and stronger than concurrent Phe level, related to increased N75 amplitudes, suggesting abnormalities in attention, and longer P110 latencies, indicating a reduction in speed of neural processing, possibly due to deficits in myelination or reduced dopamine levels in brain and retina. Similarly, higher lifetime Phe levels and Index of Dietary Control (IDC) were associated with decreased MMN amplitudes, suggesting a reduced ability to respond to stimulus change and poorer triggering of the frontally mediated attention switch. In summary, the present study in children with PKU investigated bottom-up information processing, i.e., triggered by external events, a fundamental prerequisite for the individual's responsiveness to the outside world. Results provide evidence that quality of dietary control may affect the optimal development of these pre-attentive processes, and suggest the existence of windows of vulnerability to Phe exposure.

We compared the pre-attentive processing in patients with a major depressive disorder (MDD) and matched healthy controls as indexed by the visual mismatch negativity (vMMN) elicited by exposure duration of visual stimuli randomly presented on both peripheral visual fields. To obtain the memory-comparison-based visual MMN, the role of standard and deviant stimuli was reversed in separate blocks. Compared with healthy participants, MDD patients exhibited decreased MMN amplitudes of long duration deviant only and this deficit was not correlated with the depression severity. These data suggests functional impairment of pre-attentive basic visual information processing in MDD patients.

The mismatch negativity (MMN) is observed following rare or unique sensory events, and reflects pre-attentional sensory processing of unexpected stimuli. The MMN is altered in several mental illnesses, including post-traumatic stress disorder (PTSD), but did not yield consistent results. We measured MMN in 27 survivors of the Wenchuan earthquake, including 13 who were diagnosed with PTSD, to determine if pre-attentive processing in the auditory cortex was altered by this disease. The amplitude of MMN was significantly greater in the PTSD group compared to the control group. In contrast, no significant group difference was found in the N1 potential, an event-related potential that reflects cortical transmission of sensory information. These results demonstrated an increased sensitivity to deviant stimuli in PTSD that may reflect a chronic state of hyperarousal and hypervigilance in trauma victims.

Pre‐attentive registration of aberrations in predictable sound patterns is attributed to the temporal cortex. However, electrophysiology suggests that frontal areas become more important when deviance complexity increases. To play an instrument in an ensemble, professional musicians have to rely on the ability to detect even slight deviances from expected musical patterns and therefore have highly trained aural skills. Here, we aimed to identify the neural correlates of experience‐driven plasticity related to the processing of complex sound features. We used functional magnetic resonance imaging in combination with an event‐related oddball paradigm and compared brain activity in professional musicians and non‐musicians during pre‐attentive processing of melodic contour variations. The melodic pattern consisted of a sequence of five tones each lasting 50 ms interrupted by silent interstimulus intervals of 50 ms. Compared to non‐musicians, the professional musicians showed enhanced activity in the left middle and superior temporal gyri, the left inferior frontal gyrus and in the right ventromedial prefrontal cortex in response to pattern deviation. This differential brain activity pattern was correlated with behaviorally tested musical aptitude. Our results thus support an experience‐related role of the left temporal cortex in fast melodic contour processing and suggest involvement of the prefrontal cortex. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.

Background Chinese tones are considered important in Chinese discrimination. However, the relevant reports on auditory central mechanisms concerning Chinese tones are limited. In this study, mismatch negativity (MMN), one of the event related potentials (ERP), was used to investigate pre-attentive processing of Chinese tones, and the differences between the function of oddball MVM and that of control MMN are discussed. Methods Ton subjects (six men and four women) with normal hearing participated in the study. A sequence was presented to these subjects through a loudspeaker, the sequence included four blocks, a control block and three oddball blocks. The control block was made up of five components (one pure tone and four Chinese tones) with equiprobability. The oddball blocks were made up of two components, one was a standard stimulus (tone 1) and the other was a deviant stimulus (tone 2 or tone 3 or tone 4). Electroencephalogram (EEG) data were recorded when the sequence was presented and MMNs were obtained from the analysis of the EEG data. Results Two kinds of MMNs were obtained, oddball MMN and control MMN. Oddball MMN was obtained by subtracting the ERP elicited by standard stimulation (tone 1) from that elicited by deviant stimulation (tone 2 or tone 3 or tone 4) in the oddball block; control MMN was obtained by subtracting the ERP elicited by the tone in control block, which was the same tone as the deviant stimulation in the oddball block, from the ERP elicited by deviant stimulation (tone 2 or tone 3 or tone 4) in the oddball block. There were two negative waves in oddball MMN, one appeared around 150 ms (oddball MMN 1), the other around 300 ms (oddball MMN 2). Only one negative wave appeared around 300 ms in control MMN, which was corresponding to the oddball MMN 2. We performed the statistical analyses in each paradigm for latencies and amplitudes for oddball MMN 2 in discriminating the three Chinese tones and reported no significant differences. But the latencies and amplitudes for control MMN in discriminating the three tones all were significantly different. Conclusions There are evident waveforms for oddball and control MMN obtained in normal hearing persons, indicating that the change of Chinese tones could be detected in the pre-attentive stage. Because control MMN can eliminate reflects for physical characteristics of sound, it is the genuine memory-based pre-attentive processing. Since control MMN can reflect the differences of Chinese tones processing better than oddball MMN, it is more sensitive in evaluating pre-attentive processing in Chinese tones discrimination.

In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream.

Is apparent object size represented in pre-attentive vision and can it influence visual search for size-defined targets in a spatially parallel manner? This question was investigated, using the Muller-Lyer illusion. Observers searched for a target line that was longer than the distractor lines. Test lines could be presented without context arrows (control); be adjoined by obtuse-angle context arrows (arrow heads pointing inward), making the lines appear longer; or by acute-angle arrows (heads pointing outward), making the lines appear shorter. These apparent-length modulations were larger for the target than for the distractor lines, thereby increasing and, respectively, decreasing the target-distractor length contrast. In line with these changes in contrast, target detection was found to be expedited by obtuse-angle arrows and impeded by acute-angle arrows, independently of the number of elements in the display. This finding provides further evidence for the pre-attentive processing of apparent object size.

The main goal of this review is to elucidate up to what extent pre-attentive auditory information processing is affected during human sleep. Evidence from event-related brain potential (ERP) studies indicates that auditory information processing is selectively affected, even at early phases, across the different stages of sleep-wakefulness continuum. According to these studies, 3 main conclusions are drawn: (1) the sleeping brain is able to automatically detect stimulus occurrence and trigger an orienting response towards that stimulus if its degree of novelty is large; (2) auditory stimuli are represented in the auditory system and maintained for a period of time in sensory memory, making the automatic-change detection during sleep possible; and (3) there are specific brain mechanisms (sleep-specific ERP components associated with the presence of vertex waves and K-complexes) by which information processing can be improved during non-rapid eye movement sleep. However, the remarkably affected amplitude and latency of the waking-ERPs during the different stages of sleep suggests deficits in the building and maintenance of a neural representation of the stimulus as well as in the process by which neural events lead to an orienting response toward such a stimulus. The deactivation of areas in the dorsolateral pre-frontal cortex during sleep contributing to the generation of these ERP components is hypothesized to be one of the main causes for the attenuated amplitude of these ERPs during human sleep.

A. Oehman and J. J. F. Soares (1994) demonstrated that masked presentation of phobic pictures produces increased skin conductance responses (SCRs) in phobic Ss. Oehman (1993) explained this phenomenon in terms of a hypothetical "feature detector" that identifies physical characteristics of stimuli and activates the arousal system without involving significance evaluation or consciousness. This explanation was tested by exposing 41 Ss with spider phobia (mean age 32 yrs) to spider words, general threat words, and neutral words instead of pictures. Words were presented both masked and unmasked while electrodermal activity was measured. Under unmasked conditions, SCRs were largest for spider words followed by general threat words, then neutral words. When masked, the difference between spider words and general threat words disappeared but SCRs remained significantly smaller for neutral words. The authors conclude that activation of the arousal system by masked threat cues does not necessarily depend on their perceptual characteristics.

Feature singleton search is faster when the target-defining dimension is repeated, rather than changed, across trials (Found & Müller, 1996). A similar dimension repetition benefit has been observed in a non-search (discrimination) task with a single stimulus (Mortier, Theeuwes, & Starreveld, 2005). Two experiments examined whether these effects in the two tasks originate from the same or different processing stages. Experiment 1 revealed differential feature-specific effects, and Experiment 2 differential processing of dimensionally redundant target signals between the two types of task. These dissociations support the existence of separable, pre-attentive and post-selective sources of inter-trial effects in the two tasks.

In a dichotic listening situation stimuli were presented one at a time and at random to either ear of the subject at constant inter-stimulus intervals of 800 msec. The subject's task was to detect and count occasional slightly different stimuli in one ear. In Experiment 1, these ‘signal’ stimuli were slightly louder, and in Experiment 2 they had a slightly higher pitch, than the much more frequent, ‘standard’, stimuli. In both experiments signals occured randomly at either ear. Separate evoked potentials from three different locations were recorded for each of the four kinds of stimuli (attended signals, unattended signals, attended standards, unattended standards). Contrary to Hillyard et al. (1973), no early (N 1 component) evoked-potential enhancement was observed to stimuli to the attended ear as compared with those to the unattended ear, but there was a later negative shift superimposed on potentials elicited by the former stimuli. This negative shift was considered identical to the N 1 enhancement of Hillyard and his colleagues which in the present study was forced, by the longer inter-stimulus interval used, to demonstrate temporal dissociation with the N 1 component. The ‘Hillyard effect’ was, consequently, explained as being caused by a superimposition of a CNV kind of negative shift on the evoked potential to the attended stimuli rather than by a growth of the ‘real’ N 1 component of the evoked potential.