A closer look at four-dot masking of a foveated target.

Four-dot masking with a common onset mask was recently demonstrated in a fully attended and foveated target (Filmer, Mattingley & Dux, 2015). Here, we replicate and extend this finding by directly comparing a four-dot mask with an annulus mask while probing masking as a function of mask duration, and target-mask separation. Our results suggest that while an annulus mask operates via spatially local contour interactions, a four-dot mask operates through spatially global mechanisms. We also measure how the visual system's representation of an oriented bar is impacted by a four-dot mask, and find that masking here does not degrade the precision of perceived targets, but instead appears to be driven exclusively by rendering the target completely invisible.

Masking with faces in central visual field under a variety of temporal schedules.

With a few exceptions, previous studies have explored masking using either a backward mask or a common onset trailing mask, but not both. In a series of experiments, we demonstrate the use of faces in central visual field as a viable method to study the relationship between these two types of mask schedule. We tested observers in a two alternative forced choice face identification task, where both target and mask comprised synthetic faces, and show that a simple model can successfully predict masking across a variety of masking schedules ranging from a backward mask to a common onset trailing mask and a number of intermediate variations. Our data are well accounted for by a window of sensitivity to mask interference that is centered at around 100 ms.

Increment thresholds for radial frequency trajectories produce a dipper function.

Radial frequency (RF) trajectories are a new class of stimuli that have been developed to study the visual perception of periodic motion (Or et al., 2011). These stimuli are described by a moving dot that traces a distorted path through space with periodic radial deformations whose frequency, amplitude, and phase can be independently specified. Here, we extend Or et al.'s findings by investigating how the discrimination of RF amplitude changes as a function of different reference amplitudes in a two-interval forced choice task. Using an RF3 trajectory (a pattern with three cycles of deformation along its trajectory), increment thresholds were measured at six different reference amplitudes: Detection (discriminating a circle from RF3), 1X (discriminating a pair of RF3 patterns, with the amplitude of one member of this pair set to (1X) threshold obtained from the detection condition), 2.5X, 5X, 10X, and 15X. Data show that sensitivity to changes in amplitude improves at 2.5X by a factor of about 2, recovers to detection threshold levels at 5X, and continues to rise at 10X and 15X. These results generalize across both radial frequency and the angular speed of the trajectory, and persist with low contrast trajectories. Our findings point to the existence of a neural mechanism that is sensitive to deviations from circular motion trajectories.

The face viewpoint aftereffect: adapting to full faces, head outlines, and features.

There is strong evidence that higher visual areas in the brain encode face viewpoint. The current study aims to shed light on the nature of this representation. Using a psychophysical adaptation paradigm based on Fang and He (2005), we compared the effects of adapting to full faces, head outline only, and internal features only, while testing with full faces in each case (12 subjects). We found reliable viewpoint aftereffects in all three conditions. The combined magnitude of the aftereffects from the two partial conditions was less than the aftereffect from full faces, suggesting a nonlinear combination of internal features and head outline. In a second experiment, we found that changing the direction of eye gaze did not modulate the viewpoint aftereffect.

Digits affect actions: the SNARC effect and response selection.

The SNARC (spatial-numerical association of response codes) effect refers to the finding that processing digits can modulate response times, with low digits facilitating left responses and high digits facilitating right responses. Recent evidence indicates that the locus of this effect is in the response selection stage. To examine this possibility, we presented participants with low or high digits and then asked them to make one of two keypresses (left or right) - whichever one they felt more comfortable making. The results showed that low digits biased the selection of left keypresses while high digits biased the selection of right keypresses. Thus, the SNARC effect not only affects how fast responses can be initiated but also affects what responses will be selected.