Purpose: Adaptation to female faces makes a gender-neutral test face appear male, and vice versa (Webster et al, 2004). While it may not be clear which features define “maleness” or “femaleness” in faces (Webster et al, 2004) or biological motion (Jordan, Fallah & Stoner, 2006), the assumption is that adaptation shifts the viewer’s judgment along a single perceptual dimension. Perceptual adaptation effects have been extended beyond gender to many other dimensions depicted by faces, e.g. identity, race, viewpoint, expression, attractiveness etc. However, it remains unknown whether perceptual adaptation can occur for more than a single dimension.    

Method and Results: The first study tested whether gender adaptation is observed to children’s faces. On each block of trials, participants were adapted to either boy or girl faces for a period before judging a morphed test face as predominantly a boy or a girl. Participants were more likely to report gender neutral stimuli as a girl after adaptation to the faces of boys and vice versa. This clearly replicates studies showing gender adaptation for adult faces. Like adults, the faces of boys and girls appear to be represented along a single gender dimension.

The second study tested the relationship between the representation of young (boys/girls) and mature (men/women) males and females. The adapter and test stimuli comprised all possible pairs of gender/age combinations. Adaptation was observed simultaneously across both gender and age. The relationship between age and gender adaptation effects, and its implications for neuronal representation will be discussed.   

Funded by: Atkinson Minor Research Grant to HJ

Object- and Location-based Inhibition of Return to Superimposed Surfaces

Previous studies have suggested the existence of spatial and object-based Inhibition of Return (IOR) effects, and proposed that they are driven by separate mechanisms. These studies have exclusively used objects occurring in spatially separate locations. Thus the object-based effects could be mediated by a location-based mechanism. To control for location, we superimposed two objects (random dot kinetograms). This study examines whether IOR is present for objects that are superimposed or requires that the objects are separated in space. We modified the traditional dynamic IOR displays (Tipper et al, 1991) by placing 2 superimposed surfaces in each of two peripheral locations (left vs right). Location-based IOR was observed regardless whether the target appeared on the cued or uncued surface. Critically, object-based IOR was not present; instead we found evidence of object-based facilitatory effects. Thus location-based but not object-based IOR is found with superimposed surfaces. In Experiment 2, we asked whether spatial separation is necessary throughout the trial or at time of cueing. These results have implications for the relative roles of subcortical oculomotor (e.g. superior colliculus) and cortical substrates for mediating IOR.

Do the hands shift the eyes?

 Bimodal visual-tactile receptive fields have been found attached to body parts, such as the hand. Later studies have shown that visual attention has been modulated by the nearby presence of a hand. Based on the evidence for oculomotor control of visual spatial attention, we asked whether the attentional modulation produced near the hand is integrated into the oculomotor system/saliency map. Subjects were tasked with fixating a spot on the screen. That spot disappeared as another appeared and subjects shifted their gaze to the new spot. In one experiment, on half of the trials, the subject’s hand was placed near the midpoint of the saccade trajectory, palm facing towards it. On the other half of the trials, the subject’s hand was placed on the lap. In a second experiment, on half of the trials the subject’s hand was placed near the midpoint of the saccade trajectory, palm facing towards it.  On the other half of the trials, the hand was again placed near the midpoint of the saccade, however the palm faced away from it. We analyzed the metrics of the saccades to see if hand proximity and palm/back of hand facing affected saccade trajectories. If attentional modulation produced by the hand is independent of oculomotor control of visual spatial attention, then hand proximity and facing should have no effect on saccade trajectories. However, we find effects of hand position on saccade trajectories, suggesting that the bimodal visual-tactile receptive fields are part of an integrated visual spatial attention mechanism controlled by the oculomotor system.

Selection of Superimposed Surfaces by Density

Bottom-up attention is driven by stimulus features, which may be occurring at the level of the object or the feature itself. Most studies investigating stimulus-driven selection have used spatially separate stimuli and thus are confounded by spatial mechanisms. To investigate whether it is spatial or object-based, we superimposed two surfaces (random dot kinetograms, RDKs). We asked whether dot density, previously found to be involved in bottom-up attention, can also drive object-based selection in the absence of spatial mechanisms. Superimposing two surfaces of different densities places both densities at the same spatial location and thus, those densities are separated only by the surface on which they appear.

We performed 2 experiments to investigate the effect of density on surface selection. In experiment 1, subjects fixated a central dot and an aperture with a single surface of dots moving left or right appeared in the periphery. After a random period of time, the fixation spot disappeared which was the cue for the subjects to saccade to the aperture. The density of the surface varied trial-by-trial from 0.24-30.6 dots/deg^2. Saccading to the surface resulted in an automatic pursuit of that surface. We found that pursuit speed varied with surface density. In experiment 2, one surface again varied in density while a second surface was placed in the aperture, moving at the same speed in the opposite direction and of a constant density. We varied the opposing surface’s density across sessions (range: 0.24-1.9 dots/deg^2). As the relative difference in density between the two surfaces decreased, the gain of pursuit to the higher density surface decreased. At equal densities, no pursuit occurred. These findings are consistent with competitive circuitry between the two surfaces. Overall, these results suggest that density is a salient object feature that can drive automatic selection, regardless of location-based mechanisms.

Illia Tchernikov^1,2, Mazyar Fallah^1,2
1Centre for Vision Research, York University
²School of Kinesiology & Health Science, York University

Bottom-up attention is driven by stimulus features, however most studies have not distinguished whether it is occurring at the level of the object or the feature itself. This is because those studies employed spatially separate stimuli. To study object-based selection, we superimposed two surfaces (random dot kinetograms, RDKs) to control for location-based mechanisms. Another advantage of using this paradigm is that RDKs have a set of well defined parameters which allows us to vary different features (e.g. speed) systematically. We performed 3 experiments to investigate the effect of speed on surface selection.  In experiment 1, subjects fixated a central dot and an aperture with a single surface of dots moving left or right appeared in the periphery. After a random period of time, the fixation spot disappeared which was the cue for the subjects to saccade to the aperture.  The speed of the surface varied trial-by-trial, from 0.6-24 deg/sec.  Saccading to the surface resulted in an automatic pursuit of that surface. Pursuit speed was proportional to surface speed. In experiment 2, a second surface was placed in the aperture, moving at a constant speed in the opposite direction. The other surface varied in speed, and pursuit was again measured. In contrast to theories suggesting that higher speeds are more salient, subjects had no preferential selection for a faster moving surface when presented with 2 superimposed surfaces moving in opposite directions. Experiment 3 varied one surface’s speed while the other surface was static.  At slow speeds, automatic pursuit was not detected.  However, at fast speeds, the moving surface was pursued even in the presence of a static surface. Overall, these findings suggest that motion is salient when presented alone or when presented against a static surface but not when presented against opposing motions.