For infants, visual orienting is the primary means of exploring the world. The efficiency of orienting undergoes dramatic developments in the first year of life, including the capacity to disengage attention and look away from salient or captivating stimuli impinging on the fovea (Hood, 1995
; Johnson, Posner, & Rothbart, 1991
). Coincident with this increasing ability to disengage, infants also improve in their ability to generate predictive eye movements (Hood & Atkinson, 1993
; Johnson et al., 1991
). One paradigm which measures flexibility in attentional switching in response to changes in the visual environment is known as the ‘gap-overlap task’.
Because orienting skills such as those measured in the gap-overlap task relate to the infant’s ability to switch attention flexibly and regulate emotional states (Posner & Rothbart, 1998
), some have suggested that early impairments in disengagement of visual attention may relate to the social-communicative deficits found in autism (Bryson et al., 2004
). Generally speaking, individuals with autism have a narrow focus of attention and interest, as well as acute perception of details (O’Riordan, Plaisted, Driver, & Baron-Cohen, 2001
). It is unclear, however, whether these phenomena are related, and whether or not they share common underlying mechanisms. According to one view, the infant’s inability to flexibly switch their locus of attention could lead to a decrease in social orienting (Bryson et al., 2004
). It has also been suggested that atypical processing of gaze found in autism may be a consequence of atypical visual attention (van der Geest, Kemner, Camfferman, Verbaten, & Van Engeland, 2001
). Although the direction of causality is difficult to establish and it is possible that difficulties in both social and non-social areas are related to a common mechanism, this pattern appears to continue into adulthood.
Several studies have suggested that task-dependent difficulties in visual attention are present in autism across the life-span, albeit to varying degrees. In adults, these difficulties are revealed in tasks requiring rapid shifting of attention to different spatial locations (Casey, Gordon, Mannheim, & Rumsey, 1993
; Courchesne et al., 1994
; Townsend, Harris, & Courchesne, 1996
; Wainwright-Sharp & Bryson, 1993
). A recent study which used identical methods with individuals of different ages showed that the latencies of visually guided saccades were atypical in children but not in adults with autism (Luna, Doll, Hegedus, Minshew, & Sweeney, 2007
), implying that compensatory mechanisms may operate later in development. Studies specifically using the gap-overlap task have demonstrated impairments in children and adults with autism both behaviorally (Landry & Bryson, 2004
; van der Geest et al., 2001
) as well as neurophysiologically (Kawakubo et al., 2007
Relatively less is understood in relation to how these attentional differences in the autism phenotype develop over time. A recent area of research focusing on infants at genetic high risk for autism has begun to address the emergent nature of autism symptoms more directly. Research on infant siblings of children diagnosed with autism spectrum disorders (ASD; hereafter ‘infant siblings’) offers this opportunity because the recurrence rate of ASD is significantly elevated above the general population (Bolton et al., 1994
). Studying infant siblings offers opportunities to understand why autism emerges in some cases and not in others, and can potentially explain variations associated with the broader autism phenotype
(BAP) found in genetic relatives of individuals with autism including siblings, who do not themselves have a diagnosis (Dalton, Nacewicz, Alexander, & Davidson, 2007
; Dawson et al., 2002
; Happé, Briskman, & Frith, 2001
; Hughes, Leboyer, & Bouvard, 1997
). Hence, understanding the precursors of these characteristics in infants would reveal the underlying mechanisms, which may extend to unaffected relatives.
Developmental accounts would suggest that problems in visual orienting are likely to be present very early on in autism (e.g., Bryson et al., 2004
) and it remains unknown if these extend to the BAP. However, because autism is diagnosed relatively late, rarely before two years of age (Charman & Baird, 2002
), the developmental process leading to these difficulties remains poorly understood. Most retrospective studies looking back at the first two years of life consistently show less orienting towards social stimuli as early as 9 months or younger in infants later diagnosed with autism as compared to those later diagnosed with developmental delay (Palomo, Belinchon, & Ozonoff, 2006
). Many of these studies also report an overall decreased level of orienting to both social and non-social stimuli, but the impairment is greater for social stimuli.
Increasingly, studies with infant siblings of children with autism have documented differences between these infants and control groups with no family history for autism within the first year of life (e.g., Elsabbagh et al., 2009
; McCleery, Allman, Carver, & Dobkins, 2007
). Zwaigenbaum and colleagues (2005)
provided preliminary evidence that impairments in attentional disengagement emerge between 6 and 12 months of age. At 6 months, infants who were later diagnosed with autism at 2–3 years could not be distinguished on this ability from the rest of the group. However, unlike controls, these infant siblings showed either no improvement or an increase in the latency of disengagement from central stimuli between 6 and 12 months of age.
In the current study, the aim was to explore this issue further by measuring orienting skills in a group of infant siblings of children with autism. We used the Gap-overlap task, which measures differences in the efficiency of orienting towards peripheral stimuli. In this task, three trial types are contrasted: Baseline, Gap, and Overlap. The Baseline condition is used to measure reaction time in a situation where the peripheral stimulus appears immediately after the disappearance of central stimuli. In the Overlap condition, the central stimulus remains visible and overlaps with the peripheral stimulus. Finally, in the Gap condition an intervening inter-stimulus interval separates the disappearance of the central stimulus and the appearance of the peripheral one. Based on contrasting these conditions, we focused on two emerging abilities: Disengagement, defined as the difference in reaction time between the Baseline condition and the Overlap condition. This measures the ability to disengage from a central stimulus to orient to a peripheral one. The second was Facilitation, which is the difference between the Baseline condition and the Gap condition. The latter facilitation arises because the infant would be cued by the gap preceding the onset of the peripheral stimulus, and could use the offset of the central stimulus as a cue to prepare their saccade to the later-occurring peripheral one. Hence, the task measured the infants’ ability to automatically orient to visual targets against competing stimuli as well as their ability to form expectations regarding the visual environment.