Words as Visual Objects: Neural and Behavioral Evidence for High-Level Visual Impairments in Dyslexia.

Developmental dyslexia is defined by reading impairments that are disproportionate to intelligence, motivation, and the educational opportunities considered necessary for reading. Its cause has traditionally been considered to be a phonological deficit, where people have difficulties with differentiating the sounds of spoken language. However, reading is a multidimensional skill and relies on various cognitive abilities. These may include high-level vision-the processes that support visual recognition despite innumerable image variations, such as in viewpoint, position, or size. According to our high-level visual dysfunction hypothesis, reading problems of some people with dyslexia can be a salient manifestation of a more general deficit of high-level vision. This paper provides a perspective on how such non-phonological impairments could, in some cases, cause dyslexia. To argue in favor of this hypothesis, we will discuss work on functional neuroimaging, structural imaging, electrophysiology, and behavior that provides evidence for a link between high-level visual impairment and dyslexia.

The development of foraging organization.

In foraging tasks, multiple targets must be found within a single display. The targets can be of one or more types, typically surrounded by numerous distractors. Visual attention has traditionally been studied with single target search tasks, but adding more targets to the search display results in several additional measures of interest, such as how attention is oriented to different features and locations over time. We measured foraging among five age groups: Children in Grades 1, 4, 7, and 10, as well as adults, using both simple feature foraging tasks and more challenging conjunction foraging tasks, with two target types per task. We assessed participants' foraging organization, or systematicity when selecting all the targets within the foraging display, on four measures: Intertarget distance, number of intersections, best-r, and the percentage above optimal path length (PAO). We found that foraging organization increases with age, in both simple feature-based foraging and more complex foraging for targets defined by feature conjunctions, and that feature foraging was more organized than conjunction foraging. Separate analyses for different target types indicated that children's, and to some extent adults', conjunction foraging consisted of two relatively organized foraging paths through the display where one target type is exhaustively selected before the other target type is selected. Lastly, we found that the development of foraging organization is closely related to the development of other foraging measures. Our results suggest that measuring foraging organization is a promising avenue for further research into the development of visual orienting.

Age differences in foraging and executive functions: A cross-sectional study.

Visual foraging tasks require participants to search for multiple targets among numerous distractors. Foraging paradigms enable insights into the function of visual attention above what has been learned from traditional single-target search paradigms. These include attentional orienting over time and search strategies involving target selection from different target types. To date, only a handful of studies have been conducted on the development of foraging abilities. Here, the foraging of five age groups-children aged 6, 9, 12, and 15 years and adults-was measured, as was their performance on various tasks assessing four subdomains of executive functions: inhibition, attentional flexibility, working memory, and problem solving. Executive functions consist of a complex network of independent but interconnected cognitive processes that regulate action-orienting and goal-directed behavior and have been shown to be connected to visual attention and attentional orienting. Our results show that foraging abilities improve dramatically from 6 to 12 years of age, when adult levels of foraging have been reached. This is evident from reduced foraging times, increasingly frequent switches between target types, lower switch costs, and reduced error rates. In addition, partial least squares structural equation modeling reveals that the age differences on the foraging tasks are predominantly indirect effects through executive functions. In other words, the development of successful foraging abilities is highly correlated with the maturation of executive functions.

Visual foraging and executive functions: A developmental perspective.

Visual foraging tasks, where participants search for multiple targets at a time, may provide a richer picture of visual attention than traditional single-target visual search tasks. To contribute to the mapping of foraging abilities throughout childhood and to assess whether foraging ability is dependent upon EF abilities, we compared the foraging of 66 children aged 4-7 years (mean age = 5.68 years, SD = 0.97 years, 33 girls), 67 children aged 11-12 years (mean age = 11.80 years, SD = 0.30 years; 36 girls), and 31 adults aged 20-37 (mean age 30.32 years, SD 4.37 years, 18 females) in Iceland, with a task involving multiple targets of different types. We also measured three subdomains of executive functions; inhibition, attentional flexibility, and working memory. Our results show that foraging improves dramatically between the preschool and middle school years, with the older children showing similar foraging abilities as adults due to greater ease of switching between target types. The older children and adults randomly switch between target templates during feature foraging, but exhaustively forage for a single target type before switching during conjunction foraging. Younger children, conversely, tended to also stick to the same target type for long runs during feature foraging, showing that they have difficulties with feature-based tasks. Switch costs were much lower for the older children than the youngest age group, and on par with those of adults, resulting in fast and efficient foraging. Lastly, we found a connection between foraging ability and both working memory and attentional flexibility, but not inhibition. Our study shows that foraging is a promising way of studying visual attention, how it changes throughout the lifespan, and how it is connected to other cognitive functions.

Understanding visual attention in childhood: Insights from a new visual foraging task.

A recently developed visual foraging task, involving multiple targets of different types, can provide a rich and dynamic picture of visual attention performance. We measured the foraging performance of 66 children aged 4-7 years, along with measures of two conceptually related constructs, self-regulation and verbal working memory. Our results show that foraging patterns of young children differ from adult patterns. Children have difficulty with foraging for two target types, not only when they are defined by a conjunction of features but, unlike adults, also when they forage simultaneously for two target types that are distinguished from distractors by a single feature. Importantly, such feature/conjunction differences between adults and children are not seen in more traditional single-target visual search tasks. Interestingly, the foraging patterns of the youngest children were slightly more adult-like than of the oldest ones, which may suggest that older children attempt to use strategies that they have not yet fully mastered. The older children were, however, able to complete more trials, during both feature and conjunction foraging. Self-regulation and verbal working memory did not seem to affect foraging strategies, but both were connected with faster and more efficient foraging. We propose that our visual foraging paradigm is a promising avenue for studying the development of visual cognitive abilities.