Development of Thesis

Learning is critical for the development of language, social and motor skills, however little is known about whether this process may be disrupted in individuals with ASD as well as how it manifests during their adolescence and adulthood. The aim of the thesis was to increase further our understanding of implicit learning of spatial context in individuals with ASD. The contribution of this thesis is that it integrates an ongoing question in the autism literature, i.e., local processing advantages, with a relatively novel area of investigation, i.e., learning and memory in autism.

The present work on implicit learning of spatial context in autism began in 2004 and was inspired by the weak central coherence theory’s proposal of impaired processing of context in autism. The contextual cueing task seemed an appropriate task for measuring how people with autism process implicitly a visual context that was highly abstract and this could also be developed to add to the existing work on processing of visual context using stimuli that were sema ntic and processes that were explicit. In the years that followed, ideas about both weak central coherence and contextual cueing changed in an important and very similar way. On the one hand, the weak central coherence became less focused on context processing being a deficit and more focused on local processing being a cognitive style. On the other hand the contextual cueing task became more known as a local processing rather than as a global processing task. These new developments led to the understanding that contextual cueing would be an appropriate task for investigating the accumulating evidence of local- global processing abnormalities in autism which prior to this had been primarily studied using Navon-type stimuli. The experiments in this thesis have

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been reported in the order that they were chronologically conducted and reflect the shift of focus from global and context processing (Experiments 1-3) to local

processing (Experiments 4-6). The average response times and standard errors across Experiments 1 to 3 and Experiments 4 to 6 can be found in Appendix 6.1 and 6.2 respectively.

6.2. Summary of Results

6.2.1. Is Implicit Learning Impaired in Autism? Evidence from Chapter 2 Experiment 1 employed the contextual cueing paradigm in its original form in individuals with and without ASD. Although the two groups were well matched in terms of chronological age and IQ the findings showed that during the first half of the experiment individuals with ASD detected targets in repeated trials more easily than those in the novel trials. However, this was true even in the very first block, which is unexpected because both types of trials should be of equal difficulty, as in this block participants encounter the displays for the very first time. The location of the targets in both sets of trials was matched and therefore it must have been the arrangement of colours and locations of the distractor items that was such that it made some of the targets in the novel trials more salient. It is also unclear, why individuals with ASD did not show the same reaction time benefit in the second half of the experiment. In sum, it was not possible to answer whether implicit learning was impaired in individuals with ASD based on the findings of this experiment, but its contribution was to highlight that the application of an improved counterbalancing is needed.

6.2.2. Intact Explicit Learning in Autism: Evidence from Chapter 3 In this chapter the contextual cueing paradigm was employed using realistic scene stimuli as the learning context. Repeated search through a particular scene exemplar

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led to faster detection of a target embedded in it and although some implicit learning may have occurred, the most parsimonious account of the type of learning that takes place in these scenes is that it is explicit (Hollingworth, 2009). In addition, memory was explicit as repeated scenes yielded better recognition compared to scenes viewed only once. In other words, the explicit memory of the scene context and layout guided attention to the areas where the target was more likely to be found.

Individuals with ASD were shown to be as able as the comparison group to use memo ry of previously seen displays in order to guide their attention towards the target location. Thus, it appears that individuals with ASD show preserved explicit memory of repeated material and are also able to memorize contextual information. However, search time was consistently slower in both experiments of explicit learning. The reasons for slower search time may be similar to the ones pertaining to abstract stimuli, which have been outlined in the discussion of chapter 4, but could additionally be related to the greater stimulus complexity that scene stimuli have, since search in the scene stimuli was even slower compared to search in non-scene stimuli. The present finding of faster search time in the ‘full coherence’ scenes

compared to the ‘intermediate coherence’, suggests that context guides attention more quickly in the former type of scenes in which recognition is faster. Recognition is faster in the high coherence scenes possibly because the visual system can exploit contextual associations more easily compared to the ‘cabinet of objects’ scenes in

which contextual associations between the objects may not be as readily available. These findings are important because they contribute to answering the question of

how fast context can affect the allocation of attention which is a matter of great debate (Oliva & Torralba, 2007).

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6.2.3. Superior Learning or Novelty Aversion? Evidence from Chapter 4 In this chapter the aim was to study implicit learning of spatial context in ASD by adapting the contextual cueing tasks in order to specify whether the repetition of local or non- local elements is more easily acquired. Two experiments were reported, one in which the local context was predictive of target location and one in which the non- local context was predictive of target location. Findings revealed that individuals with ASD showed greater learning compared to TD individuals when local context was predictive of target location, while ASD and TD individuals did not differ when non- local context was predictive of target location. However, due to a significantly slower novel trial respond ing in the ASD group, it was difficult to sustain that local processing, in the form of attention to local cues, facilitated performance in the ASD group more than it did for the comparison group. It was concluded that slower novel trial responding rather than a faster search in repeated trials drove part of the effect of superior contextual cueing in ASD and that this slower novel trial responding may reflect a form of novelty aversion.

6.2.4. Superior Implicit Learning of Local Context in Autism: Evidence from Chapter 5

Chapter 5 reported a study that monitored participants’ eye movements during visual search when the repeated configuration was made up of the whole display or only a part that was local to the target. Both of these conditions are similar in that the local parts are always repeated and so to find out whether indeed more attention is allocated to the local parts, it was necessary to obtain eye- movements data. Analysis of eye movements supported the claim that contextual cueing is a local processing task, since proportionally more attention was allocated to the local parts of the configuration. It was also found that the ASD group did not show more attention to the local parts than

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the TD group, which suggests that local processing in the contextual cueing task is not quantitatively different in the two groups.

It is possible that although both groups allocated the same amounts of

attention to the local context, people with autism were able to show greater learning in the local context condition because in this condition there are unique parts, which are parts that change across repetitions, while in the global context condition all items are common across repetitions. The hypothesis of reduced generalization (Plaisted, 2000, 2001) predicts that people with ASD are better able to process novel rather than common stimuli and therefore in accordance to this people with ASD would do better in the local rather than the global condition. However, an even more convincing interpretation is that the two groups learn according to their rewarded perceptual style. Thus, while TD individuals learn more from a global configuration the ASD group learns more from a local configuration. The finding that learning in the global

configuration is no greater than in the local condition for the ASD group, may reflect their difficulties in global processing that arise from superior local processing (Happé & Frith, 2006).

To study where eye- moveme nts occurred we measured the number of fixations as well as the distance of first fixation from the target and to study the temporal allocation of eye- movements we took measures of the duration of the initial fixation, the scan time and the duration of fixations to the target (gaze duration). Findings showed that while the two groups did not differ in terms of where eye- movements occurred they did differ in terms of the temporal aspect of eye-

movements. The ASD group showed longer durations in the first fixation and during scanning of the display, but not when fixating the target. This finding, pointed to

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possible difficulties in the disengagement of attention during the time before the target is fixated.