What is the reference in reference repulsion?

How the known reference weakens the visual oblique effect: a Bayesian account of cognitive improvement by cue influence

This paper investigates the influence of a known cue on the oblique effect in orientation identification and explains how subjects integrate cue information to identify target orientations. We design the psychophysical task in which subjects estimate target orientations in the presence of a known oriented reference line. For comparison the control experiments without the reference are conducted. Under Bayesian inference framework, a cue integration model is proposed to explain the perceptual improvement in the presence of the reference. The maximum likelihood estimates of the parameters of our model are obtained. In the presence of the reference, the variability and biases of identification are significantly reduced and the oblique effect of orientation identification is obviously weakened. Moreover, the identification of orientation in the vicinity of the reference line is consistently biased away from the reference line (i.e., reference repulsion). Comparing the predictions of the model with the experimental results, the Bayesian Least Squares estimator under the Variable-Precision encoding (BLS_VP) provides a better description of the experimental outcomes and captures the trade-off relationship of bias and precision of identification. Our results provide a useful step toward a better understanding of human visual perception in context of the known cues.

Dissociating Sensory and Cognitive Biases in Human Perceptual Decision-Making: A Re-evaluation of Evidence From Reference Repulsion

Our perception of the world is governed by a combination of bottom-up sensory and top-down cognitive processes. This often begs the question whether a perceptual phenomenon originates from sensory or cognitive processes in the brain. For instance, reference repulsion, a compelling visual illusion in which the subjective estimates about the direction of a motion stimulus are biased away from a reference boundary, is previously thought to be originated at the sensory level. Recent studies, however, suggest that the misperception is not sensory in nature but rather reflects post-perceptual cognitive biases. Here I challenge the post-perceptual interpretations on both empirical and conceptual grounds. I argue that these new findings are not incompatible with the sensory account and can be more parsimoniously explained as reflecting the consequences of motion representations in different reference frames. Finally, I will propose one concrete experiment with testable predictions to shed more insights on the sensory vs. cognitive nature of this visual illusion.

Distinct Aging Effects on Motion Repulsion and Surround Suppression in Humans

Elderly exhibit accumulating deficits in visual motion perception, which is critical for humans to interact with their environment. Previous studies have suggested that aging generally reduces neuronal inhibition in the visual system. Here, we investigated how aging affects the local intra-cortical inhibition using a motion direction discrimination task based on the motion repulsion phenomenon. Motion repulsion refers to the phenomenon by which observers overestimate the perceived angle when two superimposed dot patterns are moving at an acute angle. The misperception has been interpreted as local mutual inhibition between nearby direction-tuned neurons within the same cortical area. We found that elderly exhibited much stronger motion repulsion than young adults. We then compared this effect to how aging affects the global inter-cortical inhibition by adopting the surround suppression paradigm previously used by Betts et al. (2005). We found that elderly showed less change in the discrimination threshold when the size of a high-contrast drifting Gabor was increased, indicating reduced surround suppression compared to young adults. Our results indicate that aging may not always lead to a decrease of neuronal inhibition in the visual system. These distinct effects of aging on inhibitory functions might be one of the reasons that elderly people often exhibit deficits of motion perception in a real-world situation.

Altered motion repulsion in Alzheimer's disease

Recent research in Alzheimer’s disease (AD) indicates that perceptual impairments may occur before the onset of cognitive declines, and can thus serve as an early noninvasive indicator for AD. In this study, we focused on visual motion processing and explored whether AD induces changes in the properties of direction repulsion between two competing motions. We used random dot kinematograms (RDKs) and measured the magnitudes of direction repulsion between two overlapping RDKs moving different directions in three groups of participants: an AD group, an age-matched old control group, and a young control group. We showed that motion direction repulsion was significantly weaker in AD patients as comparing to both healthy controls. More importantly, we found that the magnitude of motion repulsion was predictive of the assessment of clinical severity in the AD group. Our results implicate that AD pathology is associated with altered neural functions in visual cortical areas and that motion repulsion deficit is a behavioral biomarker for the tracking of AD development.

Testing neuronal accounts of anisotropic motion perception with computational modelling

There is an over-representation of neurons in early visual cortical areas that respond most strongly to cardinal (horizontal and vertical) orientations and directions of visual stimuli, and cardinal- and oblique-preferring neurons are reported to have different tuning curves. Collectively, these neuronal anisotropies can explain two commonly-reported phenomena of motion perception – the oblique effect and reference repulsion – but it remains unclear whether neuronal anisotropies can simultaneously account for both perceptual effects. We show in psychophysical experiments that reference repulsion and the oblique effect do not depend on the duration of a moving stimulus, and that brief adaptation to a single direction simultaneously causes a reference repulsion in the orientation domain, and the inverse of the oblique effect in the direction domain. We attempted to link these results to underlying neuronal anisotropies by implementing a large family of neuronal decoding models with parametrically varied levels of anisotropy in neuronal direction-tuning preferences, tuning bandwidths and spiking rates. Surprisingly, no model instantiation was able to satisfactorily explain our perceptual data. We argue that the oblique effect arises from the anisotropic distribution of preferred directions evident in V1 and MT, but that reference repulsion occurs separately, perhaps reflecting a process of categorisation occurring in higher-order cortical areas.