Low spatial frequency (LSF) visual information is extracted rapidly from fearful faces, suggesting magnocellular involvement. Autistic phenotypes demonstrate altered magnocellular processing, which we propose contributes to a decreased P100 evoked response to LSF fearful faces. Here, we investigated whether rapid processing of fearful facial expressions differs for groups of neurotypical adults with low and high scores on the Autistic Spectrum Quotient (AQ). We created hybrid face stimuli with low and high spatial frequency filtered, fearful, and neutral expressions. Fearful faces produced higher amplitude P100 responses than neutral faces in the low AQ group, particularly when the hybrid face contained a LSF fearful expression. By contrast, there was no effect of fearful expression on P100 amplitude in the high AQ group. Consistent with evidence linking magnocellular differences with autistic personality traits, our non-linear VEP results showed that the high AQ group had higher amplitude K2.1 responses than the low AQ group, which is indicative of less efficient magnocellular recovery. Our results suggest that magnocellular LSF processing of a human face may be the initial visual cue used to rapidly and automatically detect fear, but that this cue functions atypically in those with high autistic tendency.

"The dress" has provoked intensive commentary among psychophysicists, especially in relation to color vision. Researchers have shown that manipulating illuminance cues can influence the perceived colors of the dress. Here we investigate whether illusory shifts in brightness can shift color perception of the dress. Drifting achromatic gratings with fast off and fast on shading profiles are known to give an illusion of brightening or darkening, respectively. We superimposed rotating sawtooth gratings on a series of dress images that morphed from extreme white/gold through to blue/black. In a sample of 18 adults (11 with white/gold dress percept and seven with blue/black percept), a two-alternative, forced-choice constant stimulus task measured the morphed image point at which each observer was equally likely to categorize the dress as white/gold or blue/black (the point of subjective equality or PSE). Despite manifest individual differences in the PSE, the two sawtooth temporal profiles consistently changed the perceived colors of the dress. Perceptual dimming shifted color categorization toward blue/black whereas perceptual brightening shifted color categorization toward white/gold. We conclude that color categorization is influenced substantially by illusory shifts in brightness.

When dissimilar images are presented to the left and right eyes, awareness switches spontaneously between the two images, such that one of the images is suppressed from awareness while the other is perceptually dominant. For over 170 years, it has been accepted that even though the periods of dominance are subject to attentional processes, we have no inherent control over perceptual switching. Here, we revisit this issue in response to evidence that top-down attention can target perceptually suppressed ‘vision for action’ representations in the dorsal stream. We investigated volitional control over rivalry between apparent motion (AM), drifting (DM) and stationary (ST) grating pairs. Observers demonstrated a remarkable ability to generate intentional switches in the AM and D conditions, but not in the ST condition. Corresponding switches in the pursuit direction of optokinetic nystagmus verified this finding objectively. We showed it is unlikely that intentional perceptual switches were triggered by saccadic eye movements, because their frequency was reduced substantially in the volitional condition and did not change around the time of perceptual switches. Hence, we propose that synergy between dorsal and ventral stream representations provides the missing link in establishing volitional control over rivalrous conscious percepts.

Electroretinogram (ERG) studies have demonstrated that the retinal response to temporally modulated fast-ON and fast-OFF sawtooth flicker is asymmetric. The response to spatiotemporal sawtooth stimuli has not yet been investigated. Perceptually, such drifting gratings or diamond plaids shaded in a sawtooth pattern appear brighter when movement produces fast-OFF relative to fast-ON luminance profiles. The neural origins of this illusion remain unclear (although a retinal basis has been suggested). Thus we presented toad eyecups with sequential epochs of sawtooth, sine-wave, and square-wave gratings drifting horizontally across the retina at temporal frequencies of 2.5-20 Hz. All ERGs revealed a sustained direct-current (DC) transtissue potential during drift and a peak at drift offset. The amplitudes of both phenomena increased with temporal frequency. Consistent with the human perceptual experience of sawtooth gratings, the sustained DC potential effect was greater for fast-OFF cf. fast-ON sawtooth. Modeling suggested that the dependence of temporal luminance contrast on stimulus device frame rate contributed to the temporal frequency effects but could not explain the divergence in response amplitudes for the two sawtooth profiles. The difference between fast-ON and fast-OFF sawtooth profiles also remained following pharmacological suppression of postreceptoral activity with tetrodotoxin (TTX), 2-amino-4-phosphonobutric acid (APB), and 2,3 cis-piperidine dicarboxylic acid (PDA). Our results indicate that the DC potential difference originates from asymmetries in the photoreceptoral response to fast-ON and fast-OFF sawtooth profiles, thus pointing to an outer retinal origin for the motion-induced drifting sawtooth brightness illusion.

More than 50 years ago, Hubel and Wiesel identified a subpopulation of geniculate magnocellular (M) neurons that are suppressed by diffuse red light. Since then, many human psychophysical studies have used red and green backgrounds to study the effects of M suppression on visual task performance, as a means to better understand neurodevelopmental disorders such as dyslexia and schizophrenia. Few of these studies have explicitly assessed the relative effects of red backgrounds on the M and P (parvocellular) pathways. Here we compared the effects of red and green diffuse background illumination on well-accepted cortical M and P signatures, both physiologically through nonlinear analysis of visual evoked potentials (VEPs; N = 15), and psychophysically through pulsed and steady pedestal perceptual thresholds (N = 9 with gray pedestals and N = 8 with colored pedestals). Red surrounds reduced P-generated temporal nonlinearity in the VEPs, but they did not influence M-generated VEP signatures. The steady and pulsed pedestal results suggest that red surrounds can have different effects on M and P contrast sensitivities, depending on whether the target is colored gray or red, presented centrally or peripherally, or whether it is brighter or dimmer than the surround. Our results highlight difficulties in interpreting the effects of red backgrounds on human VEPs or perception in terms of M specific suppression.

It has been suggested that differences in binocular rivalry switching rates and mixed percept durations in ASD could serve as a biomarker of excitation/inhibition imbalances in the autistic brain. If so, one would expect these differences to extend to neurotypical groups with high vs. low levels of autistic tendency. Previous studies did not detect any correlations between binocular rivalry dynamics and Autism Spectrum Quotient (AQ) scores in neurotypical control groups; however it is unclear whether this was due to the characteristics of the rivalry stimuli that were used. We further investigated this possibility in a sample of neurotypical young adults. The binocular rivalry stimuli were simple gratings, complex objects, or scrambled objects, which were presented dichoptically, either at fixation or in the periphery. A Bayesian correlation analysis showed that individuals with higher AQ scores tended to have lower perceptual switching rates for the centrally presented, simple grating rival stimuli. However, there was no evidence of a relationship between AQ and switching rates, reversal rates or mixed percept durations for any of the other binocular rivalry conditions. Overall, our findings suggest that in the non-clinical population, autistic personality traits are not a strong predictor of binocular rivalry dynamics.

Nonlinear analysis of the multifocal cortical visual evoked potential has allowed the identification of neural generation of higher-order nonlinear components by magnocellular and parvocellular neural streams. However, the location of individual brain sources that make such contributions to these evoked responses has not been studied. Thus, an m-sequence pseudorandom stimulus system was developed for use in magnetoencephalographic (MEG) studies. Five normal young adults were recorded using an Elekta TRIUX MEG with 306 sensors. Visual stimuli comprised a nine-patch dartboard stimulus, and each patch fluctuated between two luminance levels with separate recordings carried out at low (24 %) and high (96 %) temporal contrast. Sensor-space analysis of MEG evoked fields identified components of the first- and second-order Wiener kernel decomposition that showed qualitative similarity with EEG-based cortical VEP recordings. The first slice of the second-order response (K2.1) was already saturated at 24 % contrast, while the major waveform of the second slice of the second-order response (K2.2) grew strongly with contrast, consistent with properties of the magnocellular and parvocellular neurons. Minimum norm estimates of cortical source localization showed almost simultaneous activation of V1 and MT+ activations with latencies only a little greater that those reported for first neural spikes in primate single cell studies. Time-frequency analysis of the kernel responses from five minimum norm estimate scout sources shows contributions from higher-frequency bands for the first compared with the second slice response, consistent with the proposed neural sources. In support of this magno/parvo break-up, the onset latencies of the K2.2 responses were delayed by approximately 30 ms compared with K2.1 responses.

Sensory deficits are a feature of autism and schizophrenia, as well as the upper end of their non-clinical spectra. The mismatch negativity (MMN), an index of pre-attentive auditory processing, is particularly sensitive in detecting such deficits; however, little is known about the relationship between the visual MMN (vMMN) to facial emotions and autism and schizophrenia spectrum symptom domains. We probed the vMMN to happy, sad, and neutral faces in 61 healthy adults (18–40 years, 32 female), and evaluated their degree of autism and schizophrenia spectrum traits using the Autism Spectrum Quotient (AQ) and Schizotypal Personality Questionnaire (SPQ). The vMMN to happy faces was significantly larger than the vMMNs to sad and neutral faces. The vMMN to happy faces was associated with interpersonal difficulties as indexed by AQ Communication and Attention to Detail subscales, and SPQ associated with more interpersonal difficulties. These data suggest that pre-attentive processing of positive affect might be more specific to the interpersonal features associated with autism and schizophrenia. These findings add valuable insights into the growing body of literature investigating symptom-specific neurobiological markers of autism and schizophrenia spectrum conditions.