The current project investigated the brain-behavior relationships between fusiform volume and orthographic processing in children with Reading Disability (RD) and Attention-Deficit/Hyperactivity Disorder (ADHD). It was hypothesized that there would be differences in fusiform volume between those with and without RD. Individuals with and without ADHD were not expected to differ in fusiform volume and an interaction in the RD/ADHD group was not expected. Children with RD/ADHD were expected to have similar volumes to children who have RD. It also was hypothesized that size of the left fusiform segments would be correlated with three orthographic processing tasks and tests of reading achievement (i.e., Orthographic Choice, Homophone/Pseudohomophone Choice and the Colorado Perceptual Speed Task; Letter Word Identification, Word Attack, and Reading Fluency). Results indicated that there were no group differences in fusiform volume between children with and without RD as well as with and without ADHD. There were also no relationships between the left fusiform and any of the orthographic or reading achievement measures. However, all three measures of orthographic processing were significantly related to the right posterior fusiform. Additionally, Homophone/Pseudohomophone Choice and Reading Fluency demonstrated a trend with the right anterior fusiform. The findings reported in this study were largely unexpected and suggest that further research examining the relationship between right fusiform volume and orthographic processing is warranted.

Can the brain register the emotional valence of brief exposures of complex natural stimuli under conditions of forward and backward masking, and under conditions of attentional competition between foveal and peripheral stimuli? To address this question, three experiments were conducted. The first, a behavioural experiment, measured subjective valence of response (pleasant vs unpleasant) to test the perception of the valence of natural images in brief, masked exposures in a forward and backward masking paradigm. Images were chosen from the International Affective Picture System (IAPS) series. After correction for response bias, responses to the majority of target stimuli were concordant with the IAPS ratings at better than chance, even when the presence of the target was undetected. Using functional magnetic resonance imaging (fMRI), the effects of IAPS valence and stimulus category were objectively measured on nine regions of interest (ROIs) using the same strict temporal restrictions in a similar masking design. Evidence of affective processing close to or below conscious threshold was apparent in some of the ROIs. To further this line of enquiry, a second fMRI experiment mapping the same ROIs and using the same stimuli were presented in a foveal (‘attended’) peripheral (‘to-be-ignored’) paradigm (small image superimposed in the centre of a large image of the same category, but opposite valence) to investigate spatial parameters and limitations of attention. Results are interpreted as showing both valence and category specific effects of ‘to-be-ignored’ images in the periphery. These results are discussed in light of theories of the limitations of attentional capacity and the speed in which we process natural images, providing new evidence of the breadth of variety in the types of affective visual stimuli we are able to process close to the threshold of conscious perception.

Die Verarbeitung unbekannter und visuell vertrauter Gesichter wurde mittels simultaner Messung von Elektroenzephalogramm (EEG), Magnetoenzephalogramm (MEG) und Verhaltensreaktionen untersucht. Dipollokalisationen zeigten, dass MEG und EEG bei 170 ms und 400 bis 500 ms nach Beginn von Gesichterdarbietungen Aktivierung der posterioren Gyri fusiformes (GF) abbilden. Damit konnten beide Zeitbereiche als Aktivität des fusiformen Gesichterareals interpretiert werden. In einem Primingparadigma wurde bei viermaliger Wiederholung unbekannter Gesichter ein Reaktionszeitpriming gezeigt, das für Wiederholungen mit einem Zeitabstand (Lag) von Sekunden stärker als für mehrere Minuten war. Im EEG bewirkten nur Wiederholungen mit kurzem Lag einen Wiederholungseffekt von 300 ms bis 600 ms an posterioren und zentralen Elektroden. Dieser wurde als Korrelat impliziter Gedächtnisverarbeitung von Gesichtern im GF interpretiert. Ein frontaler Wiederholungseffekt ab 700 ms wurde als Ausdruck inzidentellen Erkennens der Gesichterwiederholungen angesehen. Das MEG zeigte posterior einen Wiederholungseffekt ab 800 ms für das kurze Lag. Für das lange Lag wurden keine MEG- oder EEG-Effekte gefunden. Die Wiederholung des Primingexperimentes mit den in einem Lerntraining vertraut gewordenen Gesichtern erzeugte eine generelle Verkürzung der Reaktionszeiten, aber eine Abschwächung des Primingeffektes für das kurze Lag und einen Verlust der Abhängigkeit der Primingstärke vom Zeitabstand. Diese Veränderungen gingen im EEG mit dem Trend zur Verstärkung des posterioren Wiederholungseffektes ab 500 ms einher. Im MEG konnte für die vertrauten Gesichter ein dem EEG in Zeit und Entstehungsort analoger Wiederholungseffekt gezeigt werden. Die Ergebnisse der Untersuchung von Priming bringen Evidenz für die Existenz von Primingeffekten für unbekannte Gesichter. Sie zeigen die Abhängigkeit der Primingeffekte vom Wiederholungsabstand und die Veränderung von Primingeffekten beim Erwerb visueller Vertrautheit. / The processing of unfamiliar and visually familiar faces was examined in a simultaneous measurement of Electroencephalogram (EEG), Magnetoencephalogram (MEG) and behavioural reactions during the presentation of a priming task. Dipole modelling on the EEG and MEG data localized activity in posterior fusiform gyri around 170 ms and between 400 and 500 ms post stimulus onset. Both time ranges were interpreted as activity correlates of the fusiform face area. In the priming paradigm unfamiliar faces were repeated four times. A reaction time priming effect could be shown. This effect was stronger for a short lag (seconds) between repetitions than for minutes. In EEG, only repetitions with short lag evoked a repetition effect at posterior and central electrodes between 300 and 600 ms. This effect was interpreted as a correlate of implicit memory processes presumably generated in the fusiform gyrus. A frontal repetition effect starting around 700 ms was considered a reflection of the incidental recognition of the face repetitions. The MEG data showed a repetition effect for the short lag starting at 800 ms. No electrophysiological effects of face repetition were found for the long lag. Some months later, the same subjects were visually familiarized with the faces in three learning sessions and the priming experiment was repeated. An overall shortening of reaction times was found together with a weakening of the priming effect for the short lag and an absence of the lag’s influence on the strength of the priming effects. In the EEG data a trend for a strengthening of the posterior repetition effect from 500 ms onward emerged. The MEG data yielded a repetition effect for the familiar faces that was analogous to the EEG effect. The results of the priming task give evidence for the existence of priming effects for unfamiliar and familiar faces. They furthermore demonstrate the dependency of priming effects on the lag between repetitions and the visual familiarity of the faces.

A inferência do curso temporal da atividade neural a partir do efeito BOLD é um importante problema, ainda em aberto. A forma da curva BOLD não reflete diretamente as características temporais da atividade eletrofisiológica dos neurônios. Nessa tese, é introduzido o conceito de tempo de processamento neural (TPN) como um dos parâmetros do modelo biofísico da função de resposta hemodinâmica (HRF). O objetivo da introdução desse conceito é obter estimativas mais acuradas da duração da atividade neural a partir do efeito BOLD, que possui auto grau de nãolinearidade. Duas formas de estimar os parâmetros do modelo do efeito BOLD foram desenvolvidas. A validade e aplicabilidade do conceito de TPN e das rotinas de estimação foram avaliadas por simulações computacionais e análise de séries temporais experimentais. Os resultados das simulações e da aplicação foram comparados com medidas da forma da HRF. O experimento analisado consistiu em um paradigma de tomada de decisão na presença de distratores emocionais. Esperase que o TPN em áreas sensoriais primárias seja equivalente ao tempo de apresentação de estímulos. Por outro lado, o TPN em áreas relacionadas com a tomada de decisão deve ser menor que a duração dos estímulos. Além disso, o TPN deve depender da condição experimental em áreas relacionadas ao controle de distratores emocionais. Como predito, o valores estimados do TPN no giro fusiforme foram equivalentes à duração dos estímulos e o TPN no giro do cíngulo dorsal variou com a presença de distrator emocional. Observou-se ainda lateralidade do TPN no córtex pré-frontal dorsolateral. As medidas da forma da HRF obtidas por um método convencional não dectectaram as variações observadas no TPN / The extraction of information about neural activity dynamics related to the BOLD signal is a challenging task. The temporal evolution of the BOLD signal does not directly reflect the temporal characteristics of electrical activity of neurons. In this work, we introduce the concept of neural processing time (NPT) as a parameter of the biophysical model of the hemodynamic response function (HRF). Through this new concept we aim to infer more accurately the duration of neuronal response from the highly nonlinear BOLD effect. We describe two routines to estimate the parameters of the HRF model. The face validity and applicability of the concept of NPT and the estimation procedures are evaluated through simulations and analysis of experimental time series. The results of both simulation and application were compared with summary measures of HRF shape. We analysed an experiment based on a decision-making paradigm with simultaneous emotional distracters. We hypothesize that the NPT in primary sensory areas is approximately the stimulus presentation duration. On the other hand, the NPT in brain areas related to decisionmaking processes should be less than the stimulus duration. Moreover, in areas related to processing of an emotional distracter, the NPT should depend on the experimental condition. As predicted, the NPT in fusiform gyrus is close to the stimulus duration and the NPT in dorsal anterior cingulate gyrus depends on the presence of an emotional distracter. Interestingly, the estimated NPTs in the dorsolateral prefrontal cortex indicate functional laterality of this region. The analysis using standard measures of HRF did not detect the variations observed in our method (NPT)

A inferência do curso temporal da atividade neural a partir do efeito BOLD é um importante problema, ainda em aberto. A forma da curva BOLD não reflete diretamente as características temporais da atividade eletrofisiológica dos neurônios. Nessa tese, é introduzido o conceito de tempo de processamento neural (TPN) como um dos parâmetros do modelo biofísico da função de resposta hemodinâmica (HRF). O objetivo da introdução desse conceito é obter estimativas mais acuradas da duração da atividade neural a partir do efeito BOLD, que possui auto grau de nãolinearidade. Duas formas de estimar os parâmetros do modelo do efeito BOLD foram desenvolvidas. A validade e aplicabilidade do conceito de TPN e das rotinas de estimação foram avaliadas por simulações computacionais e análise de séries temporais experimentais. Os resultados das simulações e da aplicação foram comparados com medidas da forma da HRF. O experimento analisado consistiu em um paradigma de tomada de decisão na presença de distratores emocionais. Esperase que o TPN em áreas sensoriais primárias seja equivalente ao tempo de apresentação de estímulos. Por outro lado, o TPN em áreas relacionadas com a tomada de decisão deve ser menor que a duração dos estímulos. Além disso, o TPN deve depender da condição experimental em áreas relacionadas ao controle de distratores emocionais. Como predito, o valores estimados do TPN no giro fusiforme foram equivalentes à duração dos estímulos e o TPN no giro do cíngulo dorsal variou com a presença de distrator emocional. Observou-se ainda lateralidade do TPN no córtex pré-frontal dorsolateral. As medidas da forma da HRF obtidas por um método convencional não dectectaram as variações observadas no TPN / The extraction of information about neural activity dynamics related to the BOLD signal is a challenging task. The temporal evolution of the BOLD signal does not directly reflect the temporal characteristics of electrical activity of neurons. In this work, we introduce the concept of neural processing time (NPT) as a parameter of the biophysical model of the hemodynamic response function (HRF). Through this new concept we aim to infer more accurately the duration of neuronal response from the highly nonlinear BOLD effect. We describe two routines to estimate the parameters of the HRF model. The face validity and applicability of the concept of NPT and the estimation procedures are evaluated through simulations and analysis of experimental time series. The results of both simulation and application were compared with summary measures of HRF shape. We analysed an experiment based on a decision-making paradigm with simultaneous emotional distracters. We hypothesize that the NPT in primary sensory areas is approximately the stimulus presentation duration. On the other hand, the NPT in brain areas related to decisionmaking processes should be less than the stimulus duration. Moreover, in areas related to processing of an emotional distracter, the NPT should depend on the experimental condition. As predicted, the NPT in fusiform gyrus is close to the stimulus duration and the NPT in dorsal anterior cingulate gyrus depends on the presence of an emotional distracter. Interestingly, the estimated NPTs in the dorsolateral prefrontal cortex indicate functional laterality of this region. The analysis using standard measures of HRF did not detect the variations observed in our method (NPT)