Effects of motor restrictions on preparatory brain activity.

Modifying established motor skills is a challenging endeavor due to proactive interference from undesired old to desired new actions, calling for high levels of cognitive control. Motor restrictions may facilitate the modification of motor skills by rendering undesired responses physically impossible, thus reducing demands to response inhibition. Here we studied behavioral and EEG effects of rule changes to typing in skilled touch-typists. The respective rule change-typing without using the left index finger-was either implemented per instruction only or with an additional motor restriction. In both groups, the rule change elicited delays and more errors in typing, indicating the occurrence of proactive interference. While stimulus-locked ERPs did not exhibit prominent effects of rule change or group, response-locked ERPs revealed that the time courses of preparatory brain activity preceding typing responses depended on the presence of motor restriction. Although further research is necessary to corroborate our findings, they indicate a novel brain correlate that represents changes in inhibitory response preparation induced by short-term motor restrictions.

Electrophysiological correlates underlying interference control in motor tasks.

Changing pre-existing, automatized motor skills often requires interference control. Prepotent response inhibition - one subdimension of inhibition - has been theorized to be particularly associated with successful interference control in motor skills. Recent evidence suggests that different inhibition subdimensions elicit distinct ERP patterns (with larger P3 components for response inhibition). Therefore, we examined whether a similar ERP pattern would arise in a task demanding participants to overcome interference emerging from strong motor automatisms. This was realized within a typing paradigm involving a letter switch manipulation which is able to produce strong, immediate interference effects. Most importantly, stimulus-locked ERP analyses revealed an enhanced P3 component at frontal, central and most pronouncedly parietal sites for interference trials, in line with previous reported patterns for response inhibition. Together, different analyses provide first insights into the electrophysiological correlates of motor skill change, corroborating the pivotal role of response inhibition for successful interference control.

1/f(p) Characteristics of the Fourier power spectrum affects ERP correlates of face learning and recognition.

We investigated the influence of Fourier power spectrum (1/f(p)) characteristics on face learning while recording ERPs that are associated with the representation of faces. Two image sets with an altered 1/f(p) characteristics were created. The first set consisted of stimuli with a STEEP SLOPE (1/f(3.5)) and therefore enhanced low spatial frequencies (LSF) and attenuated high spatial frequencies (HSF). The second set consisted of stimuli with a SHALLOW SLOPE (1/f(2)), similar to complex natural scenes and artwork, resulting in enhanced HSF and attenuated LSF. Faces with a SHALLOW SLOPE elicited larger N170 and N250 amplitudes and larger old/new effects for central positivity in comparison to unmodified faces. The opposite effect was observed for faces with a STEEP SLOPE that led to slower reaction times. This result suggests that diminishing the ratio of fine detail (HSF) to coarse structures (LSF) impairs face learning, whereas increasing it facilitates neurocognitive correlates of face learning.

Familiarity enhances invariance of face representations in human ventral visual cortex: fMRI evidence.

Face recognition across different viewing conditions is strongly improved by familiarity. In the present study, we tested the hypothesis that the neural basis of this effect is a less view-dependent representation of familiar faces in ventral visual cortex by assessing priming-related fMRI repetition effects. 15 healthy volunteers made male/female judgements on familiar (famous) and unfamiliar (novel) faces preceded by the same image, a different image of the same face, or another (unprimed) face. Reaction times revealed priming by same and different images independent of familiarity and more pronounced for same than different images. In the imaging data, a main effect of prime condition was found in bilateral fusiform and orbitofrontal regions. A right anterior fusiform region expressed stronger response decreases to repetition of familiar than unfamiliar faces. Bilateral mid-fusiform areas showed stronger response decreases to repetition of same than different images. A regions-of-interest analysis focussing specifically on face responsive regions suggested differences in the degree of image dependency across fusiform cortex. Collapsing across familiarity, there was greater image dependency of repetition effects in right than left anterior fusiform, replicating previous imaging findings obtained with common objects. For familiar faces alone, there was greater generalisation of repetition effects over different images in anterior than middle fusiform. This suggests a role of anterior fusiform cortex in coding image-independent representations of familiar faces.

Human brain potential correlates of voice priming and voice recognition.

This study investigated repetition priming in the recognition of famous voices, recording reaction times (RTs) and event-related brain potentials (ERPs). In Experiment 1, a facilitation was found in RTs to famous but not to unfamiliar voices when these had been primed by a different voice sample of the same speaker earlier in the experiment. However, ERPs to both famous and unfamiliar voices showed repetition priming in terms of an increased P2 component, which is thought to be generated in the auditory cortex. When the likelihood of conscious retrieval of primes was reduced in Experiment 2, facilitatory priming in RTs was again observed for famous voices, but inhibitory priming was now observed for unfamiliar voices. This is consistent with predictions of a bias model of priming. Moreover, substantial priming was observed even when voice primes were backward speech samples, which were recognised at chance levels. The results suggests that (a) voice priming is mediated to a large extent by frequency characteristics of a particular voice, rather than by articulatory and other 'sequential' features that are eliminated in backward speech; (b) priming affects the processing of voices in auditory cortical areas within 200 ms after voice onset; and (c) explicit recognition of a voice in the priming phase is not a necessary condition for priming to occur.

Priming the access to names of famous faces.

There is a continuing controversy in models of face identification concerning the level of access to names relative to semantic information. In order to determine whether names are accessed sequentially after or in parallel to semantic information, we studied participants' speeded decisions about famous faces that were primed by partial semantic or partial name information. Decisions that required the access to the celebrity's name (one or more forename syllables, Expt 1) were significantly primed by partial name primes (initials or name fragments). However, at variance with sequential stage models, no reliable priming was observed by partial semantic primes (information about nationality, occupation, or whether a person was dead or alive). Moreover, there was a clear and consistent priming effect by partial semantic primes if the task was a nationality (British or American) decision that required the access to semantic information (Expt 2), demonstrating the effectiveness of these primes. The effects of partial name primes on nationality decisions were less consistent, with a significant effect for name fragments but not initials. However, effects of name primes were generally greater for syllable decisions than nationality decisions, and effects of semantic primes were generally greater for nationality decisions than syllable decisions. Taken together, these results favour a model of parallel rather than sequential access and suggest some degree of independence in the access to personal semantics and names.

Implicit perception in patients with visual neglect: lexical specificity in repetition priming.

Twelve patients with left-sided neglect, five patients with left-sided hemianopia, and 16 matched controls performed lexical decisions for foveally presented target words or pseudowords. Target words or pseudowords could be preceded by the same stimuli, presented for 150 ms as primes in either the left (LVF) or the right (RVF) visual hemifield. Primes in the RVF caused similar levels of priming across the three groups. In contrast, whereas primes in the affected LVF did not cause priming in hemianopic patients, patients with neglect showed highly significant priming from LVF primes, and the level of priming from these neglected primes was increased relative to normal control levels. This priming effect was attributed to lexical access, because no repetition priming was observed for pronounceable pseudowords. In striking contrast to the priming results, neglect patients' explicit recognition performance for these prime stimuli was at chance for the left hemifield, although it was near perfect for the right hemifield. This demonstrates that the observed priming effects in the left hemifield were indeed caused by stimuli that were not explicitly perceived.

Neuropsychological impairments in the recognition of faces, voices, and personal names.

In order to determine the dissociability of face, voice, and personal name recognition, we studied the performance of 36 brain-lesioned patients and 20 control subjects. Participants performed familiarity decisions for portraits, voice samples, and written names of celebrities and unfamiliar people. In those patients who displayed significant impairments in any of these tests, the specificity of these impairments was tested using corresponding object recognition tests (with pictures of objects, environmental sounds, or written common words as stimuli). The results showed that 58% of the patients were significantly impaired in at least one test of person recognition. Moreover, 28% of the patients showed impairments that appeared to be specific for people (i.e., performance was preserved in the corresponding object recognition test). Three patients showed a deficit that appeared to be confined to the recognition of familiar voices, a pattern that was not described previously. Results were generally consistent with the assumption that impairments in face, voice, and name recognition are dissociable from one another. In contrast, there was no clear evidence for a dissociability between deficits in face and voice naming. The results further suggest that (a) impairments in person recognition after brain lesions may be more common than was thought previously and (b) the patterns of impairment that were observed can be interpreted using current cognitive models of person recognition (Bruce & Young, 1986; Burton, Bruce, & Johnston, 1990).

[Hemisphere asymmetry in repetitive priming and associative priming]. / Hemisphärenasymmetrien bei Wiederholungspriming und assoziativem Priming.

This study investigated hemispheric asymmetries in repetition priming (Experiment 1) and associative priming (Experiment 2) in visual word recognition. Participants performed speeded lexical decisions for foveally presented target words that could be preceded by prime words presented to the left (LVF) or right (RVF) visual field. Experiment 1 demonstrated larger repetition priming in reaction times when prime words were presented to the RVF (left hemisphere). In contrast, no repetition priming was observed for pseudowords. Hemispheric asymmetries in word repetition priming may therefore reflect the superiority of the left hemisphere in activating lexical representations. Experiment 2 did not find any hemispheric asymmetries in associative priming. The results suggest that repetition priming and associative priming act on different levels in word recognition, for which different hemispheric asymmetries exist.

Asymmetric dependencies in perceiving identity and emotion: experiments with morphed faces.

We investigated whether an asymmetric relationship between the perception of identity and emotional expressions in faces (Schweinberger & Soukup, 1998) may be related to differences in the relative processing speed of identity and expression information. Stimulus faces were morphed across identity within a given emotional expression, or were morphed across emotion within a given identity. In Experiment 1, consistent classifications of these images were demonstrated across a wide range of morphing, with only a relatively narrow category boundary. At the same time, classification reaction times (RTs) reflected the increased perceptual difficulty of the morphed images. In Experiment 2, we investigated the effects of variations in the irrelevant dimension on judgments of faces with respect to a relevant dimension, using a Garner-type speeded classification task. RTs for expression classifications were strongly influenced by irrelevant identity information. In contrast, RTs for identity classifications were unaffected by irrelevant expression information, and this held even for stimuli in which identity was more difficult and slower to discriminate than expression. This suggests that differences in processing speed cannot account for the asymmetric relationship between identity and emotion perception. Theoretical accounts proposing independence of identity and emotion perception are discussed in the light of these findings.

Asymmetric relationships among perceptions of facial identity, emotion, and facial speech.

Effects of variation in an irrelevant stimulus dimension on judgments of faces with respect to a relevant dimension were investigated. Dimensions were identity, emotional expression, and facial speech. The irrelevant dimension was correlated with, constant, or orthogonal to the relevant one. Reaction times (RTs) were predicted to increase over these conditions to the extent that the relevant dimension could not be processed independently of the irrelevant one. RTs for identity judgments were independent of variation in expression or facial speech, but RTs for expression and facial speech judgments were influenced by identity variation. Facial speech perception was affected by identity even when variation in the mouth region was eliminated. Moreover, observers could judge speech faster for personally familiar faces than for unfamiliar faces. The results suggest asymmetric dependencies between different components of face perception. Identity is perceived independently of, but may exert an influence on, expression and facial speech analysis.

Specificity of face recognition: recognition of exemplars of non-face objects in prosopagnosia.

We investigated whether the recognition deficits of two patients with long-standing prosopagnosia would also extend to exemplars within visually homogeneous object categories other than faces. Categorical object recognition was unimpaired in both patients. One patient was impaired in recognizing exemplars within both "living" and "nonliving" object categories. In contrast, the other patient performed at normal levels in exemplar recognition. These results provide further evidence that prosopagnosia does not necessarily reflect a general disorder in exemplar recognition, but can be a face-specific deficit.

The phonological loop model of working memory: an ERP study of irrelevant speech and phonological similarity effects.

The phonological loop model for retention of auditory verbal material in working memory, developed by Baddeley, assumes that irrelevant speech and phonological similarity influence only one and the same element of the system--that is, the phonological short-term store. We tested this idea by recording event-related potentials (ERPs) to auditorily presented letters that were phonologically similar or dissimilar and were to be memorized in the presence of more or less disturbing irrelevant speech. Irrelevant speech and phonological similarity caused ERP effects with clearly different scalp topographies, indicating that these factors influence different brain systems and hence probably different cognitive elements. Moreover, ERPs indicated that the phonological similarity effect might involve processes at the level of phonological analysis. Our data also support recent suggestions that the irrelevant speech effect is not based on the phonological similarity between relevant and irrelevant material, but on the phonological variability within the irrelevant stream.

Recognizing famous voices: influence of stimulus duration and different types of retrieval cues.

The current investigation measured the effects of increasing stimulus duration on listeners' ability to recognize famous voices. In addition, the investigation studied the influence of different types of cues on the naming of voices that could not be named before. Participants were presented with samples of famous and unfamiliar voices and were asked to decide whether or not the samples were spoken by a famous person. The duration of each sample increased in seven steps from 0.25 s up to a maximum of 2 s. Voice recognition improvements with stimulus duration were with a growth function. Gains were most rapid within the first second and less pronounced thereafter. When participants were unable to name a famous voice, they were cued with either a second voice sample, the occupation, or the initials of the celebrity. Initials were most effective in eliciting the name only when semantic information about the speaker had been accessed prior to cue presentation. Paralleling previous research on face naming, this may indicate that voice naming is contingent on previous activation of person-specific semantic information.

Differential localization of brain systems subserving memory for names and faces in normal subjects with event-related potentials.

Evidence from brain-damaged patients suggests different memory systems for verbal and nonverbal stimuli which also have different neuroanatomical substrates. We explored whether the scalp topographies of event-related potentials (ERPs) might confirm the dissociability of these systems. Unfamiliar faces and names were presented in separate conditions, study blocks alternating with recognition blocks. During recognition the familiarity of each stimulus was rated on a 4-point scale. The amplitudes of the ERPs to the study items were monotonically related in size to the mean subsequent familiarity ratings. Memory-related ERP differences (Dm) were calculated by subtracting ERPs recorded during the study phase to items with low subsequent familiarity ratings from items with high familiarity ratings. The Dm for faces and names showed stimulus-specific scalp topographies between 400 and 800 ms. These findings confirm that memory for names and faces is mediated by at least partially different brain systems.

Personal name recognition and associative priming in patients with unilateral brain damage.

This study investigated the performance of left- (LBD) and right-brain-damaged (RBD) patients in recognizing personal names under different conditions of associative priming. Subjects performed speeded familiarity decisions for names of famous and unfamiliar persons. These target names were preceded by primes, either faces or names, which could be neutral, related (e.g. Gorbachev-Jelzin), or unrelated (e.g. Travolta-Carter). Overall impairments in name recognition were observed in both patient groups relative to controls but were more severe in LBD than in RBD patients. This suggests that, contrary to previous hypotheses, the recognition of personal names is more dependent on left hemisphere functioning. In controls and LBD patients, associative priming effects did not differ significantly between face and name primes. In RBD patients, however, associative priming from names was larger than priming from faces. This specificity of priming effects for names in RBD patients was tentatively related to their impairments in face recognition.

Covert face recognition in prosopagnosia: a dissociable function?

Covert face recognition was investigated in a patient with prosopagnosia without object agnosia. This patient performed well in various face processing tasks like expression analysis and feature processing and had relatively preserved semantic knowledge about persons, but was slightly impaired in the visual matching of unfamiliar faces. In face-name paired-associate relearning task, covert face recognition was demonstrated to be above-chance. However, as this task cannot be meaningfully applied to control subjects, results do not necessarily indicate that the degree of covert face recognition is normal. In fact, in contrast to control subjects, the patient showed significantly reduced associative priming of names by face primes as compared to name primes, suggesting a quantitative reduction of covert face recognition. It is argued that these results support the view that overt and covert face recognition are brought about by the same functional system (Farah, O'Reilly and Vecera, 1993).

Metamemory, distinctiveness, and event-related potentials in recognition memory for faces.

A neglected topic in metamemory research is the ability of subjects to predict their own recognition performance for faces. We investigated whether subjects can make such judgments of learning (JOL) for unfamiliar faces and whether JOLs relate to facial distinctiveness, a powerful determinant of face recognition. One group of subjects made JOLs, and a second group rated the same faces for distinctiveness; subsequently, both groups tried to recognize these faces among new faces. There was significant prospective metamemory for faces that appeared to be based on facial distinctiveness. Both prospective metamemory and distinctiveness ratings related to long-lasting effects in event-related brain potentials (ERPs), closely resembling an ERP component that predicted face recognition. Therefore, the brain processes underlying JOLs, distinctiveness, and recognition memory for faces appear to be intimately related.

Event-related potentials and models of performance asymmetries in face and word recognition.

Performance asymmetries in divided visual field studies may be ascribed either to hemispheric differences in processing efficiency or to the costs of interhemispheric transfer towards the superior hemisphere. In order to distinguish between these alternatives, event-related potentials (ERPs) were recorded while subjects had to recognize laterally presented faces or words. As expected, behavioural left- and right-field advantages were observed for faces and words, respectively. Regardless of stimulus type, the ERPs displayed a sustained temporo-parietal negativity over the hemisphere stimulated directly via the contralateral hemifield. Both this hemifield-dependent negativity (HDN) and the performance asymmetries diminished to insignificance when the same stimuli were presented but subjects simply made a left-right decision about stimulus location. We conclude that the HDN is no obligatory, stimulus-bound ERP component but depends on lateralized cognitive processing. The stimulus-unspecific and time-invariant topography of the HDN might indicate that it relates to the allocation of processing resources to the directly stimulated hemisphere. The findings suggest that both faces and words were processed predominantly in the directly stimulated hemisphere, supporting an efficiency explanation of the performance asymmetries.

Reaction time improvements with practice in brain-damaged patients.

This study investigated practice effects on reaction time (RT) in patients with unilateral brain damage and age-matched controls. Subjects performed a Sternberg-type stimulus recognition task. Both RT and RT variability decreased in all subjects from a short initial session to a second session, 1 to 3 days later. Within the second session, however, RT remained constant in the controls, whereas it was further reduced in the patients. These findings argue against the assumption that brain-damaged patients generally show smaller practice effects on RT than controls, and instead suggest that it may be essential to provide patients with sufficient practice opportunities. To locate the processing stage where practice is effective, analyses were performed also on the intercept and slope parameters of the RT function. It is argued that the differential practice effects were due to the speeding of perceptual and/or response-related stages, rather than gains in memory search speed.