Pseudoneglect is the tendency to be biased towards the left side of space in tasks of a spatial nature. A non-visual form of the bias referred to as ‘representational pseudoneglect’ has been observed when people generate a mental representation of a stimulus in the complete absence of visual input - participants pay more attention to the left-hand side of the mental representation. The aim of this thesis was to advance our understanding of representational pseudoneglect by exploring the bias across lifespan using different modes of non-visual presentation (touch vs. audition vs. visual imagery). In Experiments 1 and 2 healthy participants aged 3 to 96 years used touch alone without vision to bisect wooden rods at the perceived centre. All participants (with the exception of some adolescents) showed leftward biases on tactile rod bisection and significant gender and age effects were found. In Experiments 3 to 10 healthy young adults listened to aural-verbal descriptions of abstract patterns or real-world scenes without vision and formed a mental representation of the spatial layout that was described. A leftward bias was consistently found for a relative judgement task along with a significant effect of monaural presentation and start side, but no lateralised bias for memory recall regardless of ‘mental mapping’ ability or method of response. In Experiment 11 participants eye movements were recorded while they visually processed and then memorised natural real-world scenes; again there was no lateralised memory or eye movement bias. Experiment 12 showed that a secondary task increased the magnitude of visuo-spatial pseudoneglect for children and adults under certain conditions. This thesis argues that purely representational forms of pseudoneglect clearly exist in healthy participants and that: 1) the results can be explained in terms of contralateral attentional orienting by the right hemisphere, 2) extraneous variables (gender; physical or imagined starting position) can mediate representational pseudoneglect, and 3) current models of cognitive ageing need to provide for a cognitive bias that can be enhanced by age.

Neurologically healthy individuals misbisect their visual space by erring towards the left. This misreprentation has been attributed to the right hemisphere dominance in processing of spatial information. Lateral biases are thought to emerge as behavioural outcomes of cognitive processing, mainly attention. Recently, attention mechanisms have been reported to be closely inter-related to memory systems, where attention directs what will be remembered and memory impacts where attention is directed. Although spatial biases attributed to attention have been widely accepted, the claim that memory exhibits similar biases has been more controversial. Recent research shows that recall of representations is biased towards the left side of space, indicating that lateral asymmetries may not necessarily be limited to perceptual and attentional mechanisms, but may extend to memory mechanisms as well. The purpose of this work is to understand better the relationship between lateral biases within working memory and attention interactions. Two approaches were considered. First, working memory, as defined by the representations and operations related to manipulate the representations, used time delay and visual load. Second, backward masking was used to control the relative formation of the working memory trace, which strengthens with recurrence of the visual stimuli and is through to progress from attention to working memory. To explore these two theoretical avenues, a novel task was constructed. Two circular arrays were presented at the top and bottom of the computer screen. These arrays were composed of six individual discs of varying shade. Hence, the overall array represented a greyscale gradient, where discs on one lateral side were darker compared to the middle discs and the other lateral side. For example, if two darkest discs were presented on the left side, the lightest discs were presented on the right side. Such array was presented with its left/right mirror reversed image. In this example, the second array was with the lightest discs on the left side and growing progressively darker, with darkest discs on the right side. Such presentation requires the participants to integrate the array of individual discs into an overall representation to perform a brightness judgement and select the array seemingly darker. A total of six behavioural studies addressed the two theoretical approaches. The first approach, to determine the impact of inter-stimulus time interval and visual load on lateral asymmetries, was addressed in four experiments. The findings indicated that participants were able to integrate the discrete disks into an overall array. Participants exhibited an overall leftward bias similar to that obtained in attention tasks, where they selected an array to be overall darker when the darkest disks were presented on the left side of the array. Furthermore, these biases increased the most when the stimuli were presented in the lower half of the computer screen, consistent with the lower visual field. Conversely, stimuli presented to the upper half of the screen elicited a rightward bias, which is consistent with the upper visual field. Stronger biases were observed when the stimulus noise, in the form of black, white and grey pixels, was relatively low and weaker biases were attained with a relatively high noise levels. In the second study, the findings showed that the magnitude of upper and lower visual field biases shows dependence on the vertical and lateral stimulus manipulation within these fields. Upper-left, lower-right interactions indicate that biases may not simply rely on the horizontal and vertical dimensions, as previously thought, but also on the relative spatial distribution of stimuli within these dimensions. The third study, which used the standard rectangular greyscale stimuli, revealed that visual load does not impact the lateral biases, but shows to impact the upper and lower visual field processing. Further, time interval between stimulus presentation and response, extended past 1 second eliminated lateral and vertical biases. The remaining two studies investigated lateral asymmetries within working memory by selectively manipulating the formation of working memory trace using backward masks. The presence of a mask, following a stimulus, inhibits the memory trace formation for that stimulus. Conversely, if no mask is presented following the stimuli, the memory trace is permitted to form within working memory. Again, using the circular array task, participants were required to select the overall darker array while retaining either a shade of position information from the array within their working memory. Findings showed increased rightward biases when memory trace was permitted to form with longer inter-stimulus (3 sec) time interval, as compared to shorter (0 to 1 sec) time interval. In the last study, the participants were required to make brightness judgement while maintaining either a position or shade information within working memory to determine whether previously acquired information, which does not serve as a cue, impact the brightness judgement task. Rightward biases were evident when participants were required to maintain either a position or shade information relating to the array, but did not provide any cue-type of information, which could facilitate performance. Rightward biases were stronger while retaining position information and completing the brightness task, hence indicating a spatial nature of the bias. As well, stronger rightward biases were obtained when the to-be-remembered position information was allowed to create a memory trace. Furthermore, recall accuracy of the position information was increased when the memory trace was permitted to form, indicating involvement of working memory processes. Overall, the data attained in this set of experiments can be interpreted using the activation-orientation model presented by Reuter-Lorenz (1990) indicating that this model may also be valuable when integrating working memory in addition to attentional processes.

The human visual system has learned to assume that light originates from above, most likely because of the persistent natural overhead light source – the sun (Ramachandran, 1988). Asymmetries of perception in neurologically normal individuals, like assuming light is coming from above, in part result from efficiency measures of the visual system. Not only is light assumed to come from above, but light from above and to the left has been found to decrease reaction times in target finding as well as increase aesthetic preference (Sun & Perona, 1998; Smith & Elias, 2013). The underlying cause of the bias towards upper-left lighting is debated, and may have a relationship with another peculiar phenomenon in neurologically normal individuals where greater attention is paid to leftward space, called pseudoneglect (Bowers & Heilman, 1980). Alternatively, an explanation suggesting that directional reading influences lighting preferences has been proposed, as Smith and Elias (2013) found native right-to-left readers to be significantly different from leftward biased left-to-right readers. The current set of experiments used eye-tracking and a target finding paradigm to assess differences between left-to-right and right-to-left readers. Manipulating the position of the light illuminating a field of spheres generated targets, creating either 1 convex bubble among 15 concave depressions, or vice-versa. Results from these studies are mixed, and highlight differences between both upper and lower and lateral visual space. Light originating from above facilitated shorter average duration times for both groups, whereas left-to-right readers tended to prefer light from the upper-left, while right-to-left readers preferred light from the upper-right. No one target location in the array facilitated shorter average duration times for right-to-left readers, although left-to-right readers tended to exhibit shorter durations when identifying targets in the upper-left quadrant. Participants spent the greatest amount of time examining the upper quadrants of the array, tending to focus more on the side of the image that their native reading direction begins on. The influence of directional reading on light source perception, and the potential problems of using exclusively Western participant samples are discussed.

Made available in DSpace on 2016-03-15T19:40:03Z (GMT). No. of bitstreams: 1 Ana Clara Portela Hara.pdf: 1185473 bytes, checksum: 98af56b10b63f07c120ba7122a299358 (MD5) Previous issue date: 2013-08-06 / The human visual attention and cognitive processes involved still arouse interest in investigations and have gaps. Perform a reading task or look for a parking spot are common actions of our day-to-day life that require the recruitment of our visual attentional system. The present study aimed to investigate the influence of Transcranial Direct Current Stimulation (tDCS) over Posterior Parietal Cortex (PPC) in the performance of visuospatial attention tasks, such as Bisection of Lines test and Visual Search test in young healthy volunteers. In order to analyze differences and similarities between different types of stimulation (anodic and cathodic simulation) as well as the pseudoneglect phenomenon, participated 21 young adults of which 90.47% female, 95.23% with incomplete higher education; right handed and with a mean age of 22.66 ± 3.04 (mean ± standard deviation). The results showed that participants were faster in the second assessment compared to baseline for both tasks. In addition, volunteers were faster in the Line Bisection test when the large lines was at left. Another important finding of the study was the longer fixation time in the left visual hemifield when faced with larger lines on the left in the Line Bisection Task. Furthermore, similar results when there are target to the left or right was find in the Visual Search test. Was also observe an increase in fixation time on right hemifield after cathodal stimulation in the Visual Search test compared to baseline. Therefore, these findings come against pseudoneglect phenomenon, as well as inhibition of the right posterior parietal cortex with the Transcranial Direct Current Stimulation can have induced a decrease in this phenomenon. The present study brought important contributions to the understanding of pseudoneglect phenomenon, and showed that tDCS can be an important tool for research and future intervention possibilities. / A atenção visual humana e os processos cognitivos nela envolvidos ainda despertam interesse em investigações e apresentam lacunas. Realizar uma tarefa de leitura ou procurar uma vaga no estacionamentosão ações comuns do nosso dia-a-dia que exigem o recrutamento do nosso sistema atencional visual. O presente trabalhoteve como objetivo investigar a influência da Estimulação Transcraniana por Corrente Contínua em Córtex Parietal Posterior (CPP) no desempenho de tarefas de atenção visuoespacial, tais como Bissecção de Linhas e Busca Visual, em jovens saudáveis; a fim de analisar diferenças e semelhanças entre os diferentes tipos de estimulação (anódica, catódica e placebo), bem como o fenômeno pseudonegligência. Participaram do estudo 21 adultos jovens, sendo 90,47% do sexo feminino; 95,23% com ensino superior incompleto; destros e com idade média de 22,66 ±3,04 (média±desvio-padrão). Os resultados mostraram que na Tarefa de Bissecção de Linhas os participantes foram mais rápidos na segunda avaliação em comparação com a linha de base. Além disso, os voluntários foram mais rápidos quando diante das linhas Maiores à Esquerda. Outro achado importante do estudo foi o maior tempo de fixação visual em hemicampo esquerdo quando diante de linhas maiores à esquerda. Quanto aos resultados encontrados na Tarefa de Busca Visual, os participantes apresentaram maior número de acertos quando os alvos apareceram em hemicampo esquerdo. Além disso, independentemente da localização do alvo, seja em hemicampo esquerdo ou hemicampo direito, o tempo de fixação foi maior à esquerda. Outro achado significativo foi o aumento no tempo de fixação em hemicampo direito após estimulação catódica na tarefa Busca Visual em comparação com a linha de base. Tais achados apontam para o fenômeno pseudonegligência, assim como a inibição do CPP direito por meio da ETCC pode ter induzido a diminuição de tal fenômeno. O presente estudo trouxe importantes contribuições no entendimento da pseudonegligência, assim como demonstrou ser uma importante ferramenta de investigação sobre o fenômeno e com possibilidades futuras de intervenção.

- / Doctorat en Sciences Psychologiques et de l'éducation / info:eu-repo/semantics/nonPublished