Naira A. Taroyan

Reading words and pseudowords in dyslexia: ERP and behavioural tests in English-speaking adolescents

The study reports neurophysiological and behavioural correlates of lexical decision processes in English speaking dyslexic and non-dyslexic readers. Nine dyslexic adolescents (ages 15.6-17.8) and 9 control (ages 15.4-19.3) adolescents were tested, and the event related potentials (ERPs) to words and pseudowords were recorded simultaneously with behavioural measures. As expected, both groups showed significantly lower accuracy and longer response times for the pseudowords. Furthermore, overall performance (in terms of lower accuracy and longer response times) was significantly worse for the dyslexic group. The ERP analysis indicated that the later positive peaks, P4 (around 400 ms from stimulus onset) and P5 (around 500 ms), were significantly delayed and attenuated for the dyslexic group. Analysis of the early ERP peaks recorded in the occipitotemporal region led to an interesting dissociation. The controls showed a left lateralised Condition effect, with the amplitude of P1 significantly smaller to words than pseudowords. By contrast, there was no such lexical effect for the dyslexic group, with equal P1 amplitudes for words and pseudowords, at the control level for pseudowords. The deviations in the early ERP components of dyslexics support the evidence of deficits in pre-lexical visual word form recognition within the first 110 ms of activation together with altered hemispheric asymmetry. In addition, the slowed and attenuated late ERP components and weaker behavioural performance of the dyslexic group highlight deficits in the later, cognitive, processing stages.

Neurophysiological and behavioural correlates of coherent motion perception in dyslexia

Coherent motion perception was tested in nine adolescents with dyslexia and 10 control participants matched for age and IQ using low contrast stimuli with three levels of coherence (10%, 25% and 40%). Event-related potentials (ERPs) and behavioural performance data were obtained. No significant between-group differences were found in performance accuracy and response latencies of correct responses, for early (P1, N1, and P2) or late (P3) ERP peaks. However, attenuated early ERPs in the 10% coherent condition correlated significantly with lower performance accuracy (r = -.66) and with the magnitude of literacy deficit (r = -.46).

Exploring sequential stereopsis for co-planarity tasks

We used the sequential stereopsis paradigm and apparatus described by Enright (Vision Research, 36, (1996) 307-312). The observers task was to set targets to equidistance in Experiments 1-3, and to make them co-planar in Experiment 4. However, it is argued that in all experiments observers exploited a co-planarity setting strategy. Sequential stereopsis produced good performance throughout in terms of low disparity thresholds when head position was varied by rotations around three axes: vertical (azimuth condition); horizontal (elevation); and midline (tilt). It also produced good performance when the targets were shifted in position so that they both lay on one side of the median plane of the head. These results cannot be accounted for by Enrights isovergence hypothesis unless it is extended to incorporate other information about eye positions. Performance was better but not greatly so in control simultaneous stereopsis conditions, nor did it deteriorate much when the observers view was restricted solely to the targets by removing visibility of the room in which the apparatus was located. Target settings were typically located on a concave arc centred on the median plane. This effect was quantitatively modelled using disparity correction for a relief task of co-planarity (Gârding, Porrill, Mayhew, & Frisby. Vision Research, 35 (1995) 703-722). This modelling indicated over-estimations of c.10-20 cm in fixation distance for target distances in the range 71.5-112.5 cm.

Effect of signal length on the performance of independent component analysis when extracting the lambda wave

The aim of the study was to investigate the effect of signal length on the performance of a signal source separation method, independent component analysis (ICA), when extracting the visual evoked potential (EP) lambda wave from saccade-related electro-encephalogram (EEG) waveforms. A method was devised that enabled the effective length of the recorded EEG traces to be increased prior to processing by ICA. This involved abutting EEG traces from an appropriate number of successive trials (a trial was a set of waveforms recorded from 64 electrode locations in a study investigating saccade performance). ICA was applied to the saccade-related EEG and electro-oculogram (EOG) waveforms recorded from the electrode locations. One spatial and five temporal features of the lambda wave were monitored to assess the performance of ICA applied to both abutted and non-abutted waveforms. ICA applied to abutted trials managed to extract all six features across all seven subjects included in the study. This was not the case when ICA was applied to the non-abutted trials. It was quantitatively demonstrated that the process of abutting EEG waveforms was useful for ICA preprocessing when extracting lambda waves.

Nicotine enhances an auditory Event-Related Potential component which is inversely related to habituation.

Nicotine is a psychoactive substance that is commonly consumed in the context of music. However, the reason why music and nicotine are co-consumed is uncertain. One possibility is that nicotine affects cognitive processes relevant to aspects of music appreciation in a beneficial way. Here we investigated this possibility using Event-Related Potentials. Participants underwent a simple decision-making task (to maintain attentional focus), responses to which were signalled by auditory stimuli. Unlike previous research looking at the effects of nicotine on auditory processing, we used complex tones that varied in pitch, a fundamental element of music. In addition, unlike most other studies, we tested non-smoking subjects to avoid withdrawal-related complications. We found that nicotine (4.0 mg, administered as gum) increased P2 amplitude in the frontal region. Since a decrease in P2 amplitude and latency is related to habituation processes, and an enhanced ability to disengage from irrelevant stimuli, our findings suggest that nicotine may cause a reduction in habituation, resulting in non-smokers being less able to adapt to repeated stimuli. A corollary of that decrease in adaptation may be that nicotine extends the temporal window during which a listener is able and willing to engage with a piece of music.

Exploring the Relationship Between Callous-Unemotional Traits, Empathy Processing and Affective Valence in a General Population

Callous–Unemotional (CU) traits are personality attributes, which are associated with a deficit of affective valence and reduced empathetic responding in high CU trait clinical populations. The aim of the research was to explore whether a similar pattern of empathy and emotional responding correlated with CU trait manifestation in the general population. A total of 124 participants completed the Inventory of Callous-Unemotional Traits, the Interpersonal Reactivity Index, the Empathy Quotient, an expression recognition task, and a measure of affective response. Negative correlations with CU trait score were observed for both cognitive empathy and emotional empathy. Accuracy in the identification of fearful expressions presented a negative association with CU trait score. Self-rating of affective valence, when viewing both positive and negative images, indicated a universal reduction in emotional response associated with increased CU trait manifestation.

The accuracy of metric judgements: Perception of surface normal

Observers adjusted a probe (a short rod) to appear normal to a planar surface slanted in depth. In Experiment 1, observers (N=12) performed this metric task in two conditions: with reduced cues to calibration of binocular viewing parameters and with full cues. The results provided evidence for the use of an internal working metric in metric tasks because they confirm predictions that (i) errors should be largely systematic and accounted for by assuming an inaccurate working metric and (ii) this metric should be consistent with miscalibration of relevant viewing parameters. The data support the prediction that performance errors decrease in a manner consistent with improved binocular calibration, when better cues to relevant viewing parameters are provided. We performed two additional control experiments as further tests of the binocular miscalibration account, to determine whether performance in Experiment 1 could be explained instead by the use of monocular cues. We found that monocular performance was significantly poorer than binocular performance in reduced-cue conditions (Experiment 2) and full-cue conditions (Experiment 3). These control experiments provide confirmation that binocular cues contribute to performance in the full-cue conditions of Experiment 1, and that disparity was the only effective cue to slant in reduced-cue conditions.

Seeing is knowing? Visual word recognition in non-dyslexic and dyslexic readers: An ERP study

The aim of the current study was to investigate whether phonological/semantic processing of the word takes place simultaneously with, or following, the early processing of its visual features. Event related potentials (ERPs) were recorded in 13 dyslexic (four female) and 14 non-dyslexic (six female) native English speaking young adults in two lexical decision tasks. In Task 1 participants had to make an orthographic lexical decision to distinguish frequently used words (W) from pseudohomophones (PH1) focusing on visual properties of stimuli. In Task 2 they had to make a phonological lexical decision—to pseudohomophones (PH2) and pseudowords (PW) and decide whether stimuli sounded like real words—focusing on non-visual higher order, i.e., phonological and semantic, processing of the stimuli. The behavioural performance was less good and the ERP peaks’ latency longer in dyslexics compared to controls. The reaction times (RTs) and the number of errors (reversed for the controls in Task 2) increased across four conditions for both groups in the following order: W< PH1< PH2< PW. The ERPs were larger in Task 2 compared to Task 1 starting at 100 ms (P1) for the controls and from about 220 ms (P2) for the dyslexics. The latency of N2 peak in left occipito-temporal sites was larger (as was the number of errors) in PH2 compared to PW condition in controls only, which indicates phonological/semantic specific processing at a time latency of 250–260 ms. Thus, the visual task required less effort than the phonological task, dyslexics’ behavioural performance was less good and the brain activation delayed compared to controls. Combined behavioural and ERP results of this study indicated that phonological/semantic processing of the word took place 150 ms after processing of its visual features in controls and possibly later in dyslexics.