Reading fluency and statistical learning across modalities and domains: Online and offline measures.

The vulnerability of statistical learning has been demonstrated in reading difficulties in both the visual and acoustic modalities. We examined segmentation abilities of Hungarian speaking adolescents with different levels of reading fluency in the acoustic verbal and visual nonverbal domains. We applied online target detection tasks, where the extent of learning is reflected in differences between reaction times to predictable versus unpredictable targets. Explicit judgments of well-formedness were also elicited in an offline two-alternative forced choice (2AFC) task. Learning was evident in both the acoustic verbal and visual nonverbal tasks, both in online and offline measures, but learning effects were larger both in online and offline tasks in the verbal acoustic condition. We haven't found evidence for a significant relationship between statistical learning and reading fluency in adolescents in either modality. Together with earlier findings, these results suggest that the relationship between reading and statistical learning is dependent on the domain, modality and nature of the statistical learning task, on the reading task, on the age of participants, and on the specific language. The online target detection task is a promising tool which can be adapted to a wider set of tasks to further explore the contribution of statistical learning to reading acquisition in participants from different populations.

An event-related potential study of the testing effect: Electrophysiological evidence for context-dependent processes changing throughout repeated practice.

The testing effect refers to a special form of performance improvement following practice. Specifically, repeated retrieval attempts improve long-term memory. In the present study we examined the underlying mechanisms of the testing effect as a function of time by investigating the electrophysiological correlates of repeated retrieval practice. We additionally investigated the ERP waveforms of the repeated practice phase as a function of the accuracy on the final test in a "difference due to memory" (Dm) analysis. We found a parietally distributed, increased positive amplitude between 500 and 700 ms, and a more positive parietal wave between 700 and 1000 ms in the later relative to the early phases of retrieval practice. We found parietal Dm effects in the same two time windows in the retrieval practice condition with a more positive amplitude predicting retrieval success on the final test. We interpret the earlier waveform as a component associated with episodic recollection and the later ERP as a component related to post-retrieval evaluation processes. Our results demonstrate the important role of these retrieval-related processes in the facilitating effect of retrieval practice on later retrieval, and show that the involvement of these processes changes throughout practice.

Statistical Learning and the Effect of Starting Small in Developmental Dyslexia.

Purpose Impairments in statistical learning abilities of individuals with developmental dyslexia (DD) have been demonstrated in word segmentation and in visual artificial grammar learning (AGL) tasks, but so far, little attention has been devoted to the AGL abilities of this population in the acoustic verbal domain. This study aimed to test whether adolescents with dyslexia have difficulties in extracting abstract patterns from auditory sequences of nonsense syllables based on a finite state grammar relative to typically developing (TD) peers. We also tested whether incremental presentation of stimuli of different lengths (starting small) has a facilitating effect on learning complex structures in dyslexia (and in TD) as opposed to presenting strings in random order. Method Thirty-one adolescents with DD and 31 age-matched control participants completed an AGL task. Participants passively listened to acoustic sequences of nonsense syllables generated by an artificial grammar in the training phase. In the test phase, they were presented with pairs of novel grammatical and nongrammatical sequences and were required to decide which member of a sequence pair was more similar to the material heard during training. Results Performance levels and the proportion of learners were smaller in participants with DD than in the control group. While the starting small effect was nominally present both in performance levels and in the number of learners in participants with DD, but not in the group with TD, the presentation of strings in incremental order did not statistically improve learning performance in either group. Conclusion Our results suggest that (a) statistical learning of abstract sequences in the acoustic domain is less efficient in people with dyslexia than in TD controls and (b) while incremental presentation of stimuli of different length did not improve learning in our study, the observed pattern of results suggests that the effects of different training designs should be explored further in developmental disorders.

When noise is beneficial for sensory encoding: Noise adaptation can improve face processing.

The presence of noise usually impairs the processing of a stimulus. Here, we studied the effects of noise on face processing and show, for the first time, that adaptation to noise patterns has beneficial effects on face perception. We used noiseless faces that were either surrounded by random noise or presented on a uniform background as stimuli. In addition, the faces were either preceded by noise adaptors or not. Moreover, we varied the statistics of the noise so that its spectral slope either matched that of the faces or it was steeper or shallower. Results of parallel ERP recordings showed that the background noise reduces the amplitude of the face-evoked N170, indicating less intensive face processing. Adaptation to a noise pattern, however, led to reduced P1 and enhanced N170 amplitudes as well as to a better behavioral performance in two of the three noise conditions. This effect was also augmented by the presence of background noise around the target stimuli. Additionally, the spectral slope of the noise pattern affected the size of the P1, N170 and P2 amplitudes. We reason that the observed effects are due to the selective adaptation of noise-sensitive neurons present in the face-processing cortical areas, which may enhance the signal-to-noise-ratio.

Stimulus dependence and cross-modal interference in sequence learning.

A central issue in sequence learning is whether learning operates on stimulus-independent abstract elements, or whether surface features are integrated, resulting in stimulus-dependent learning. Using the serial reaction-time (SRT) task, we test whether a previously presented sequence is transferrable from one domain to another. Contrary to previous artificial grammar learning studies, there is mapping between pre- and posttransfer stimuli, but contrary to previous SRT studies mapping is not obvious. In the pre-transfer training phase, participants face a dot-counting task in which the location of the dots follows a predefined sequence. In the test phase, participants face an auditory SRT task in which the spatial organization of the response locations is either the same as spatial sequence in the training phase, or not. Sequence learning is compared to two control conditions: one with a non-sequential random-dot counting in the training phase, and one with no training phase. Results show that sequential training proactively interferes with later sequence learning, regardless of whether the sequence is the same or different in the two phases. Results argue for the existence of a general sequence processor with limited capacity, and that sequence structures and sequenced elements are integrated into a single sequential representation.

Electrophysiological indices of aberrant error-processing in adults with ADHD: a new region of interest.

Deficits in error-processing are postulated in core symptoms of ADHD. Our goal was to investigate the neurophysiological basis of abnormal error-processing and adaptive adjustments in ADHD, and examine whether error-related alterations extend beyond traditional Regions of Interest (ROIs), particularly to those involved in adaptive adjustments, such as the Salience Network system. We obtained event-related potentials (ERPs) during a Go/NoGo task from 22 adult-ADHD patients and 29 matched healthy controls using a high-density 256-electrode array. Error-related ERPs with error-negativity (ERN) and error-positivity (Pe) served as probes of error-processing. In ADHD patients both ERN and Pe were significantly reduced, and the reduction was associated with core psychopathological symptoms. The ERP-attenuation was prominent not only at traditional ROI-electrodes but across many other brain areas, with a distinctive subset of group-differences and symptom-correlations manifested at temporo-parietal sites, with right-lateralization. Source-localization uncovered two neural-sources for the error-related ERPs: one in the cingulate cortex near midline, which was present in both groups; and one in the right insular cortex, which was present only in the control group. The neural patterns of impairments may be the result of coexisting deficits in the dorsal midline error-processing brain network involved in "error-processing proper" and the right-lateralized temporo-parietal salience network involved in the evaluation of significance of the error-signals. Our source-localization findings potentially identify a missing link between the previously reported structural change, i.e., reduced insular volume, and the well-established behavioral deficits in ADHD.

The electrophysiological correlates of integrated face and body-part perception.

Previous studies have suggested that the human visual system processes faces and bodies holistically-that is, the different body parts are integrated into a unified representation. However, the time course of this integrative process is less known. In the present study, we investigated this issue by recording event-related potentials evoked by a face and two hands presented simultaneously and in different configurations. When the hands were rotated to obtain a biologically implausible configuration, a reduction of the P2 amplitude was observed relative to the condition in which the face and hands were retained in their veridical configuration and were supplemented with visual cues to highlight further the overall body posture. Our results show that the P2 component is sensitive to manipulations affecting the configuration of face and hand stimuli and suggest that the P2 reflects the operation of perceptual mechanisms responsible for the integrated processing of visually presented body parts.

ALTERED BOLD RESPONSE WITHIN THE CORE FACE-PROCESSING NETWORK IN CONGENITAL PROSOPAGNOSIA.

BACKGROUND AND PURPOSE: Congenital prosopagnosia is a life-long disorder of face perception. To study the neural backgrounds of congenital prosopagnosia we measured the blood oxygen level-dependent response of congenital prosopagnosic participants, using functional magnetic resonance imaging. METHODS: We tested three persons of the family (father, daughter and son), having symptoms of congenital prosopagnosia, as well as healthy controls, using combined neuropsychological and functional magnetic resonance imaging methods. To reveal the neural correlates of the impairments, blood oxygen level-dependent responses within the occipito-temporal cortex were measured to faces and nonsense object images in a block-design experiment. RESULTS: Neuropsychological tests demonstrated significant impairments of face perception/recognition in each subject. We found that the activity of the fusiform and occipital face areas as well as of the lateral occipital cortex was significantly reduced in congenital prosopagnosic participants when compared to controls. Analysis of the hemodynamic response function revealed a lower peak response, but also a significantly faster and stronger decay of the blood oxygen level-dependent response in the occipito-temporal areas in congenital prosopagnosic participants when compared to controls. CONCLUSION: Our results emphasize the dysfunction of the core face processing system, as well as the lateral occipital complex, in congenital prosopagnosia. Further, the functional impairment of these areas is signalled best by the altered hemodynamic response function, showing abnormally low initial peak and stronger and faster decay in the later parts of the blood oxygen level-dependent response.

Adaptation Duration Dissociates Category-, Image-, and Person-Specific Processes on Face-Evoked Event-Related Potentials.

Several studies demonstrated that face perception is biased by the prior presentation of another face, a phenomenon termed as face-related after-effect (FAE). FAE is linked to a neural signal-reduction at occipito-temporal areas and it can be observed in the amplitude modulation of the early event-related potential (ERP) components. Recently, macaque single-cell recording studies suggested that manipulating the duration of the adaptor makes the selective adaptation of different visual motion processing steps possible. To date, however, only a few studies tested the effects of adaptor duration on the electrophysiological correlates of human face processing directly. The goal of the current study was to test the effect of adaptor duration on the image-, identity-, and generic category-specific face processing steps. To this end, in a two-alternative forced choice familiarity decision task we used five adaptor durations (ranging from 200-5000 ms) and four adaptor categories: adaptor and test were identical images-Repetition Suppression (RS); adaptor and test were different images of the Same Identity (SameID); adaptor and test images depicted Different Identities (DiffID); the adaptor was a Fourier phase-randomized image (No). Behaviorally, a strong priming effect was observed in both accuracy and response times for RS compared with both DiffID and No. The electrophysiological results suggest that rapid adaptation leads to a category-specific modulation of P100, N170, and N250. In addition, both identity and image-specific processes affected the N250 component during rapid adaptation. On the other hand, prolonged (5000 ms) adaptation enhanced, and extended category-specific adaptation processes over all tested ERP components. Additionally, prolonged adaptation led to the emergence of image-, and identity-specific modulations on the N170 and P2 components as well. In other words, there was a clear dissociation among category, identity-, and image-specific processing steps in the case of longer (3500 and 5000 ms) but not for shorter durations (< 3500 ms), reflected in the gradual reduction of N170 and enhancement of P2 in the No, DiffID, SameID, and RS conditions. Our findings imply that by manipulating adaptation duration one can dissociate the various steps of human face processing, reflected in the ERP response.

The face evoked steady-state visual potentials are sensitive to the orientation, viewpoint, expression and configuration of the stimuli.

Previous studies demonstrated that the steady-state visual-evoked potential (SSVEP) is reduced to the repetition of the same identity face when compared with the presentation of different identities, suggesting high-level neural adaptation to face identity. Here we investigated whether the SSVEP is sensitive to the orientation, viewpoint, expression and configuration of faces (Experiment 1), and whether adaptation to identity at the level of the SSVEP is robust enough to generalize across these properties (Experiment 2). In Experiment 1, repeating the same identity face with continuously changing orientation, viewpoint or expression evoked a larger SSVEP than the repetition of an unchanged face, presumably reflecting a release of adaptation. A less robust effect was observed in the case of changes affecting face configuration. In Experiment 2, we found a similar release of adaptation for faces with changing orientation, viewpoint and configuration, as there was no difference between the SSVEP for the same and different identity faces. However, we found an adaptation effect for faces with changing expressions, suggesting that face identity coding, as reflected in the SSVEP, is largely independent of the emotion displayed by faces. Taken together, these results imply that the SSVEP taps high-level face representations which abstract away from the changeable aspects of the face and likely incorporate information about face configuration, but which are specific to the orientation and viewpoint of the face.

The background of reduced face specificity of N170 in congenital prosopagnosia.

Congenital prosopagnosia is lifelong face-recognition impairment in the absence of evidence for structural brain damage. To study the neural correlates of congenital prosopagnosia, we measured the face-sensitive N170 component of the event-related potential in three members of the same family (father (56 y), son (25 y) and daughter (22 y)) and in age-matched neurotypical participants (young controls: n = 14; 24.5 y±2.1; old controls: n = 6; 57.3 y±5.4). To compare the face sensitivity of N170 in congenital prosopagnosic and neurotypical participants we measured the event-related potentials for faces and phase-scrambled random noise stimuli. In neurotypicals we found significantly larger N170 amplitude for faces compared to noise stimuli, reflecting normal early face processing. The congenital prosopagnosic participants, by contrast, showed reduced face sensitivity of the N170, and this was due to a larger than normal noise-elicited N170, rather than to a smaller face-elicited N170. Interestingly, single-trial analysis revealed that the lack of face sensitivity in congenital prosopagnosia is related to a larger oscillatory power and phase-locking in the theta frequency-band (4-7 Hz, 130-190 ms) as well as to a lower intertrial jitter of the response latency for the noise stimuli. Altogether, these results suggest that congenital prosopagnosia is due to the deficit of early, structural encoding steps of face perception in filtering between face and non-face stimuli.

Altering second-order configurations reduces the adaptation effects on early face-sensitive event-related potential components.

The spatial distances among the features of a face are commonly referred to as second-order relations, and the coding of these properties is often regarded as a cornerstone in face recognition. Previous studies have provided mixed results regarding whether the N170, a face-sensitive component of the event-related potential, is sensitive to second-order relations. Here we investigated this issue in a gender discrimination paradigm following long-term (5 s) adaptation to normal or vertically stretched male and female faces, considering that the latter manipulation substantially alters the position of the inner facial features. Gender-ambiguous faces were more likely judged to be female following adaptation to a male face and vice versa. This aftereffect was smaller but statistically significant after being adapted to vertically stretched when compared to unstretched adapters. Event-related potential recordings revealed that adaptation effects measured on the amplitude of the N170 show strong modulations by the second-order relations of the adapter: reduced N170 amplitude was observed, however, this reduction was smaller in magnitude after being adapted to stretched when compared to unstretched faces. These findings suggest early face-processing, as reflected in the N170 component, proceeds by extracting the spatial relations of inner facial features.

Phase noise reveals early category-specific modulation of the event-related potentials.

Previous studies have found that the amplitude of the early event-related potential (ERP) components evoked by faces, such as N170 and P2, changes systematically as a function of noise added to the stimuli. This change has been linked to an increased perceptual processing demand and to enhanced difficulty in perceptual decision making about faces. However, to date it has not yet been tested whether noise manipulation affects the neural correlates of decisions about face and non-face stimuli similarly. To this end, we measured the ERPs for faces and cars at three different phase noise levels. Subjects performed the same two-alternative age-discrimination task on stimuli chosen from young-old morphing continua that were created from faces as well as cars and were calibrated to lead to similar performances at each noise-level. Adding phase noise to the stimuli reduced performance and enhanced response latency for the two categories to the same extent. Parallel to that, phase noise reduced the amplitude and prolonged the latency of the face-specific N170 component. The amplitude of the P1 showed category-specific noise dependence: it was enhanced over the right hemisphere for cars and over the left hemisphere for faces as a result of adding phase noise to the stimuli, but remained stable across noise levels for cars over the left and for faces over the right hemisphere. Moreover, noise modulation altered the category-selectivity of the N170, while the P2 ERP component, typically associated with task decision difficulty, was larger for the more noisy stimuli regardless of stimulus category. Our results suggest that the category-specificity of noise-induced modulations of ERP responses starts at around 100 ms post-stimulus.

Probabilistic sequence learning in mild cognitive impairment.

Mild Cognitive Impairment (MCI) causes slight but noticeable disruption in cognitive systems, primarily executive and memory functions. However, it is not clear if the development of sequence learning is affected by an impaired cognitive system and, if so, how. The goal of our study was to investigate the development of probabilistic sequence learning, from the initial acquisition to consolidation, in MCI and healthy elderly control groups. We used the Alternating Serial Reaction Time task (ASRT) to measure probabilistic sequence learning. Individuals with MCI showed weaker learning performance than the healthy elderly group. However, using the reaction times only from the second half of each learning block-after the reactivation phase-we found intact learning in MCI. Based on the assumption that the first part of each learning block is related to reactivation/recall processes, we suggest that these processes are affected in MCI. The 24-h offline period showed no effect on sequence-specific learning in either group but did on general skill learning: the healthy elderly group showed offline improvement in general reaction times while individuals with MCI did not. Our findings deepen our understanding regarding the underlying mechanisms and time course of sequence acquisition and consolidation.

Face distortion aftereffects evoked by featureless first-order stimulus configurations.

After prolonged exposure to a distorted face with expanded or contracted inner features, a subsequently presented normal face appears distorted toward the opposite direction. This phenomenon, termed as face distortion aftereffect (FDAE), is thought to occur as a result of changes in the mechanisms involved in higher order visual processing. However, the extent to which FDAE is mediated by face-specific configural processing is less known. In the present study, we investigated whether similar aftereffects can be induced by stimuli lacking all the typical characteristics of a human face except for its first-order configural properties. We found a significant FDAE after adaptation to a stimulus consisting of three white dots arranged in a triangular fashion and placed in a gray oval. FDAEs occurred also when the adapting and test stimuli differed in size or when the contrast polarity of the adaptor image was changed. However, the inversion of the adapting image as well as the reduction of its contrast abolished the aftereffect entirely. Taken together, our results suggest that higher-level visual areas, which are involved in the processing of facial configurations, mediate the FDAE. Further, while adaptation seems to be largely invariant to contrast polarity, it appears sensitive to orientation and to lower level manipulations that affect the saliency of the inner features.