An analysis of embedded figures test performance in individuals with austistic-like traits

The Embedded Figures Test (EFT; Witkin, Oltman, Raskin, & Karp, 1971) is a search task that involves detecting a simple closed-contour shape hidden within a complex structure. Individuals with an autism spectrum disorder (ASD) are faster detecting embedded figures relative to typically developing controls (de Jonge, Kemner, & van Engeland, 2006; Jarrold, Gilchrist, & Bender, 2005; Jolliffe & Baron-Cohen, 1997; Pellicano, Gibson, Maybery, Durkin, & Badcock, 2005). Superior EFT performance is not only observed in ASD groups relative to controls; those in the typically developing population with high levels of autistic-like traits also demonstrate enhanced performance relative to those with low levels of such traits (Grinter, Maybery et al., 2009; Grinter, Van Beek, Maybery, & Badcock, 2009; Russell-Smith, Maybery, & Bayliss, 2010). Examining individuals in these latter groups can be a useful method to extend current knowledge of complex ASDs by avoiding confounds such as comorbidity associated with ASD samples. While enhanced EFT performance linked to autism has been repeatedly observed, it is not clear what underlying mechanism(s) allow(s) for such superiority. The aim of this thesis was to examine which specific aspects of the stimuli employed in the EFT are critical to enable superior visual search performance by those with high levels of autistic-like traits. Four series of experiments compared performance of groups of individuals with either high or low levels of autistic-like characteristics, as determined by the AutismSpectrum Quotient (AQ; Baron-Cohen, Wheelwright, Skinner, Martin, & Clubley, 2001), on the EFT and on a number of novel visual tasks designed to systematically investigate potential critical components of the EFT. The first series, reported in Chapter Two, introduced a basic search task which contained radial frequency (RF) patterns as stimuli. RF patterns are deformed circular closed-contours created by sinusoidally modulating the radius of a circle, where the number of cycles of IV modulation defines the RF number. The EFT simple target shapes are closed-contours, and because considerable recent work on discrimination of closed-contours has utilised RF patterns, employing these well-defined shapes may aid clarification of the underlying processes. The task was to detect a target RF3 (triangular-shaped) pattern from an array of spatially discrete distracter RF4 (square-like) patterns. The number of distracter RF patterns was varied to provide a measure of visual search performance, specified as the change in reaction time (RT) with increasing set size (SS), commonly referred to as the gradient or slope of the linear function. Overlap of elements, one component of the EFT, was introduced to determine whether it was critical to the high AQ search advantage. Increasing overlap of elements reduced search efficiency of both groups in a systematic way, but the relative difference between the two groups‟ gradients remained the same. The high AQ group were faster overall and had a shallower gradient in all RF search conditions. They also had significantly shorter EFT RTs and fewer errors relative to the low AQ group. Performance on the RF search tasks and EFT was correlated, providing some support for the convergent validity of the RF search task. Complexity resulting from overlap does not appear to be critical to superior EFT performance in high AQ individuals. Chapter Three examined whether irrelevant segmentation, a design element of the EFT, affects the high AQ performance advantage. To create segmentation cues, the stimulus array was surrounded by a box, and two intersecting lines ending on the borders of the box were methodically introduced to the basic RF search task to mimic the role of lines in the EFT. The additional lines acted as clutter, resulting in an increase in intercept of the fitted RT versus SS function, however again the relative differences between the two groups‟ slopes were comparable regardless of whether segmenting lines were present or absent. Further, the slopes were consistently shallower for the high V AQ relative to the low AQ group. Therefore, task-irrelevant segmenting lines did not affect the performance difference between high and low AQ groups. The research reported in Chapter Four used the same RF search paradigm, but investigated the impact of changing the stimuli to contain RF patterns which engage local rather than global closed-contour processing mechanisms (Loffler, Wilson, & Wilkinson, 2003) as the targets in the EFT are also closed-contours that vary in the number of included corners, such that they may evoke either level of processing. „Local‟ and „global‟ processes have an explicit meaning in closed-contour analysis literature. Global processing, using the whole contour, can be demonstrated in low RF patterns (up to 10 cycles of modulation), whereas high RF patterns (more than 10 cycles of modulation) are processed by local mechanisms (Loffler et al., 2003). Since the EFT places targets within a complex set of different shapes, the first two experiments in Chapter Four were conducted to investigate the impact of increasing heterogeneity in the distracter set. The following two experiments were designed to determine whether the closed contour of EFT targets was essential or whether, instead, local aspects of the contours were sufficient to obtain the performance differences previously observed between high and low AQ groups. The tasks used in the four experiments produced variation in the gradients obtained and again the high AQ group had shorter EFT RTs and consistently shallower gradients on these RF search tasks. The same relative performance difference between groups was observed across the four experiments, suggesting that neither distracter heterogeneity nor the closed-contour of the target was critical. In addition, the correlation between RF search task gradients and AQ scores was stronger than the correlation between EFT RTs and AQ scores, providing support for using this new RF search task instead of the EFT in future applications. It was recently suggested that global closed-contour processing was weaker in children with an ASD relative to typically developing controls (Grinter, Maybery, VI Pellicano, Badcock, & Badcock, 2010). Chapter Five presents a study designed to investigate this proposition in groups with high or low levels of autistic-like characteristics to determine whether the global visual mechanisms processing low RF closed-contours are active to the same extent in these two groups. An RF integration task (Loffler et al., 2003) examined the improvement in discriminating between a circle and RF3 pattern as additional information (i.e., one, two, or three lobes of deformation) was presented on the closed RF3 contour. The ability to globally integrate deformation information around the RF contour was better for the high AQ group relative to the low AQ group. Performance on the RF integration task, RF search task, and EFT were correlated. Chapter Six provides a general discussion of the current findings, noting that the complexity of the stimuli created in the EFT by adding element overlap, spurious segmentation and variation in the contour properties of the target influence search performance but do not alter the difference in performance between high and low AQ groups. This leads to the conclusion that the RF search task with its capacity for repetition is a better choice for quantifying the mechanisms underlying performance differences in these groups. Chapter Six also attempts to provide unifying explanations for the available data. A critical evaluation of the findings leads to the conclusion that a single overarching explanation is unlikely. Superior EFT and RF search performance could arise if individuals with high autistic-like characteristics had a wider effective field of vision. However, this cannot account for the novel report in this thesis of superior RF integration ability in high relative to low AQ scorers. Additional work will be required to investigate the suggestion of wider effective vision and the nature of the superior integration mechanism in individuals with high autistic-like traits. The chapter ends by noting the more general point that a simplistic assertion of weaker or intact global and VII enhanced local processing is insufficient. Rather, progress is likely to be facilitated if researchers move away from the broad application of the labels „local‟ and „global‟ and instead focus on the specific underlying visual and cognitive processes required to perform the tasks.