Atypical modulation of face-elicited saccades in autism spectrum disorder in a double-step saccade paradigm

Abstract

Atypical development of face processing is a major characteristic in autism spectrum disorder (ASD), which could be due to atypical interactions between subcortical and cortical face processing. The current study investigated the saccade planning towards faces in ASD. Seventeen children with ASD and 17 typically developing (TD) children observed a pair of upright or inverted face configurations flashed sequentially in two different spatial positions. The reactive saccades of participants were recorded by eye-tracking. The results did not provide evidence of overall impairment of subcortical route in ASD, However, the upright, but not the inverted, face configuration modulated the frequency of vector sum saccades (an index of subcortical control) in TD, but not in ASD. The current results suggests that children with ASD do not have overall impairment of the subcortital route, but the subcortical route may not be specialized to face processing.

Keywords: autism spectrum disorder; double saccade; eye tracking; face processing; subcortical route; superior colliculus.

Figure 1

Design of double-step saccade paradigm. (A) A trial began with a presentation of a fixation stimulus consisting of a colourful and animating cartoon, which was followed by the brief presentation of two identical targets that flashed sequentially (80 ms each, with no overlap). Fixation positions varied in a pseudo-random order, between four possible locations: centre bottom (as shown), centre top, centre left and centre right. Targets were either upright (as shown) or upside-down face configurations. (B) Three types of responses were of critical concern: a vector sum saccade, the direction of which is equivalent to the vector summation of two target locations relative to the fovea; a retinotopic saccade consisting of two saccades, each equivalent to the positions of the targets at the time of presentation relative to the fovea; and a body-centred saccade, on to each target location. The black continuous lines represents the direction of exerted saccades, and the gray dashed lines represent the direction vector of each target at the time of presentation relative to fovea.

Figure 2

The change in mean ratio of vector sum saccades from first to second blocks for upright (black continuous lines) and inverted (grey dotted lines) face configurations for (A) typically developing children (TD) and (B) children with Autism Spectrum Disorder (ASD). error bar: standard error.