A behavioral advantage for the face pareidolia illusion in peripheral vision.

Investigation of visual illusions helps us understand how we process visual information. For example, face pareidolia, the misperception of illusory faces in objects, could be used to understand how we process real faces. However, it remains unclear whether this illusion emerges from errors in face detection or from slower, cognitive processes. Here, our logic is straightforward; if examples of face pareidolia activate the mechanisms that rapidly detect faces in visual environments, then participants will look at objects more quickly when the objects also contain illusory faces. To test this hypothesis, we sampled continuous eye movements during a fast saccadic choice task-participants were required to select either faces or food items. During this task, pairs of stimuli were positioned close to the initial fixation point or further away, in the periphery. As expected, the participants were faster to look at face targets than food targets. Importantly, we also discovered an advantage for food items with illusory faces but, this advantage was limited to the peripheral condition. These findings are among the first to demonstrate that the face pareidolia illusion persists in the periphery and, thus, it is likely to be a consequence of erroneous face detection.

Enhanced electrophysiological responses to explicitly predicted and pre-imagined inputs, with confirmation from online decoding with neuro-feedback.

Neural responses to sensory inputs can scale with the likelihood of encountering the input. This is consistent with the predictive coding framework, in that the human brain is expected to be less responsive to predicted inputs. Typically, however, prediction is not explicitly measured. It is inferred from the probability of encountering an event. When an input is explicitly predicted, responses to predicted inputs can be enhanced. Here, we ask if this effect can be ascribed to a generic priming effect, from pre-cogitating about one of two possible inputs. Consistent with this, we find that P300s (a relatively late event-related potential measured with electroencephalography) are greater for explicitly predicted audio and visual inputs, and that this effect cannot be distinguished from a priming effect from pre-imagining audio or visual presentations. Evidence indicates that participants engaged in pre-imagining presentations, as we were able to decode online what type of presentation (audio or visual) they were imagining with a high success rate (approx. 73%), and we encouraged compliance with neuro-feedback regarding this success rate. Our data confirm that human cortex can be more responsive to inputs that have been subject to pre-cogitation-including explicit predictions. This highlights that while anticipatory processes can reduce responding to likely inputs, they can also enhance responding to explicitly predicted inputs.

Predicting the subjective intensity of imagined experiences from electrophysiological measures of oscillatory brain activity.

Most people can conjure images and sounds that they experience in their minds. There are, however, marked individual differences. Some people report that they cannot generate imagined sensory experiences at all (aphantasics) and others report that they have unusually intense imagined experiences (hyper-phantasics). These individual differences have been linked to activity in sensory brain regions, driven by feedback. We would therefore expect imagined experiences to be associated with specific frequencies of oscillatory brain activity, as these can be a hallmark of neural interactions within and across regions of the brain. Replicating a number of other studies, relative to a Resting-State we find that the act of engaging in auditory or in visual imagery is linked to reductions in the power of oscillatory brain activity across a broad range of frequencies, with prominent peaks in the alpha band (8-12 Hz). This oscillatory activity, however, did not predict individual differences in the subjective intensity of imagined experiences. For audio imagery, these were rather predicted by reductions within the theta (6-9 Hz) and gamma (33-38 Hz) bands, and by increases in beta (15-17 Hz) band activity. For visual imagery these were predicted by reductions in lower (14-16 Hz) and upper (29-32 Hz) beta band activity, and by an increase in mid-beta band (24-26 Hz) activity. Our data suggest that there is sufficient ground truth in the subjective reports people use to describe the intensity of their imagined sensory experiences to allow these to be linked to the power of distinct rhythms of brain activity. In future, we hope to combine this approach with better measures of the subjective intensity of imagined sensory experiences to provide a clearer picture of individual differences in the subjective intensity of imagined experiences, and of why these eventuate.

Event Probabilities Have a Different Impact on Early and Late Electroencephalographic Measures Regarded as Metrics of Prediction.

The oddball protocol has been used to study the neural and perceptual consequences of implicit predictions in the human brain. The protocol involves presenting a sequence of identical repeated events that are eventually broken by a novel "oddball" presentation. Oddball presentations have been linked to increased neural responding and to an exaggeration of perceived duration relative to repeated events. Because the number of repeated events in such protocols is circumscribed, as more repeats are encountered, the conditional probability of a further repeat decreases-whereas the conditional probability of an oddball increases. These facts have not been appreciated in many analyses of oddballs; repeats and oddballs have rather been treated as binary event categories. Here, we show that the human brain is sensitive to conditional event probabilities in an active, visual oddball paradigm. P300 responses (a relatively late component of visually evoked potentials measured with EEG) tended to be greater for less likely oddballs and repeats. By contrast, P1 responses (an earlier component) increased for repeats as a goal-relevant target presentation neared, but this effect occurred even when repeat probabilities were held constant, and oddball P1 responses were invariant. We also found that later, more likely oddballs seemed to last longer, and this effect was largely independent of the number of preceding repeats. These findings speak against a repetition suppression account of the temporal oddball effect. Overall, our data highlight an impact of event probability on later, rather than earlier, electroencephalographic measures previously related to predictive processes-and the importance of considering conditional probabilities in sequential presentation paradigms.

The temporal visual oddball effect is not caused by repetition suppression.

The oddball paradigm is commonly used to investigate human time perception. Trains of identical repeated events ('standards') are presented, only to be interrupted by a different 'oddball' that seems to have a relatively protracted duration. One theoretical account has been that this effect is driven by repetition suppression for repeated standards. The idea is that repeated events seem shorter as they incur a progressively reduced neural response, which is supported by the finding that oddball perceived duration increases linearly with the number of preceding repeated standards. However, typical oddball paradigms confound the probability of oddball presentations with variable numbers of standard repetitions on each trial, allowing people to increasingly anticipate an oddball presentation as more standards are presented. We eliminated this by making participants aware of what fixed number of standards they would encounter before a final test input and tested different numbers of standards in separate experimental sessions. The final event of sequences, the test event, was equally likely to be an oddball or another repeat. We found a positive linear relationship between the number of preceding repeated standards and the perceived duration of oddball test events. However, we also found this for repeat tests events, which speaks against the repetition suppression account of the temporal oddball effect.

Neural correlates of visual acuity for fine text.

Human sensitivity to visual input often scales with the magnitude of evoked responses in the brain. Here, we demonstrate an exception. We record electroencephalography (EEG) while people attempt to resolve fine print - similar to people attempting to read eye charts (the world's most popular means of testing vision). We find that the ability to resolve fine print is associated with smaller evoked responses recorded by large clusters of occipital-parietal sensors ∼150 ms after people see words. Moreover, we find that a better ability to resolve fine print is associated with enhanced alpha-band oscillatory brain activity immediately prior to word presentations. These investigations were inspired by psychophysical data, which suggested the ability to resolve fine print can be enhanced by pre-adaptation to flicker, which should encourage a reduced neural response to inputs. We included this manipulation in this study, and our results are broadly consistent with this conjecture. As alpha-band activity has been linked to inhibitory interactions in visual cortex, we regard our data as evidence that smaller neural responses to fine print can be promoted by inhibitory processes that target unhelpful blur-related signals, which thereby sharpen subsequent visual experiences.

Commonalities between the Berger Rhythm and spectra differences driven by cross-modal attention and imagination.

When people close their eyes, the power of alpha-band oscillatory brain activity increases. We explored the possibility that this could be related to a suppression of visual processing, rather than being a default dynamic of the visual brain. We recorded brain activity while people meditated with their eyes open or closed, and when people attended to or imagined having auditory or visual experiences. We could decode the attended or imagined modality of experiences based on the spectra of brain activity that prevailed while meditating with open or closed eyes. We also found anecdotal evidence suggesting the strength of imagined sensory experiences may be predicted by the dynamics of neural networks that are responsive to inputs. Overall, our data suggest spectra changes when people close their eyes might relate to a targeted suppression of visual processing, as opposed to being a default state of idle visual brains.

The perceived duration of expected events depends on how the expectation is formed.

Repeated events can seem shortened. It has been suggested that this results from an inverse relationship between predictability and perceived duration, with more predictable events seeming shorter. Some evidence disputes this generalisation, as there are cases where this relationship has been nullified, or even reversed. This study sought to combine different factors that encourage expectation into a single paradigm, to directly compare their effects. We find that when people are asked to declare a prediction (i.e., to predict which colour sequence will ensue), guess-confirming events can seem relatively protracted. This augmented a positive time-order error, with the first of two sequential presentations already seeming protracted. We did not observe a contraction of perceived duration for more probable or for repeated events. Overall, our results are inconsistent with a simple mapping between predictability and perceived duration. Whether the perceived duration of an expected event will seem relatively contracted or expanded seems to be contingent on the causal origin of expectation.

Neural prediction errors depend on how an expectation was formed.

When a visual event is unexpected, because it violates a train of repeated events, it excites a greater positive electrical potential at sensors positioned above occipital-parietal human brain regions (the P300). Such events can also seem to have an increased duration relative to repeated (implicitly expected) events. However, recent behavioural evidence suggests that when events are unexpected because they violate a declared prediction-a guess-there is an opposite impact on duration perception. The neural consequences of incorrect declared predictions have not been examined. We replicated the finding whereby repetition violating events elicit a larger P300 response. However, we found that events that violated a declared prediction entrained an opposite pattern of response-a smaller P300. These data suggest that the neural consequences of a violated prediction are not uniform but depend on how the prediction was formed.

Occipital alpha-band brain waves when the eyes are closed are shaped by ongoing visual processes.

One of the seminal findings of cognitive neuroscience is that the power of occipital alpha-band (~ 10 Hz) brain waves is increased when peoples' eyes are closed, rather than open. This has encouraged the view that alpha oscillations are a default dynamic, to which the visual brain returns in the absence of input. Accordingly, we might be unable to increase the power of alpha oscillations when the eyes are closed, above the level that would normally ensue when people close their eyes. Here we report counter evidence. We used electroencephalography (EEG) to record brain activity when people had their eyes open and closed, both before and after they had adapted to radial motion. The increase in alpha power when people closed their eyes was increased by prior adaptation to a broad range of radial motion speeds. This effect was greatest for 10 Hz motion, but robust for other frequencies (and especially 7.5 Hz). This discredits a persistent entrainment of activity at the adaptation frequency as an explanation for our findings. Our data show that the power of occipital alpha-band brain waves can be increased by motion sensitive visual processes that persist when the eyes are closed. Consequently, we suggest that the power of these brain waves is, at least in part, an index of the degree to which visual brain activity is being subjected to inhibition. This is increased when people close their eyes, but can be even further increased by pre-adaptation to radial motion.

Visual predictions, neural oscillations and naïve physics.

Prediction is a core function of the human visual system. Contemporary research suggests the brain builds predictive internal models of the world to facilitate interactions with our dynamic environment. Here, we wanted to examine the behavioural and neurological consequences of disrupting a core property of peoples' internal models, using naturalistic stimuli. We had people view videos of basketball and asked them to track the moving ball and predict jump shot outcomes, all while we recorded eye movements and brain activity. To disrupt people's predictive internal models, we inverted footage on half the trials, so dynamics were inconsistent with how movements should be shaped by gravity. When viewing upright videos people were better at predicting shot outcomes, at tracking the ball position, and they had enhanced alpha-band oscillatory activity in occipital brain regions. The advantage for predicting upright shot outcomes scaled with improvements in ball tracking and occipital alpha-band activity. Occipital alpha-band activity has been linked to selective attention and spatially-mapped inhibitions of visual brain activity. We propose that when people have a more accurate predictive model of the environment, they can more easily parse what is relevant, allowing them to better target irrelevant positions for suppression-resulting in both better predictive performance and in neural markers of inhibited information processing.

An observer model of tilt perception, sensitivity and confidence.

Humans experience levels of confidence in perceptual decisions that tend to scale with the precision of their judgements; but not always. Sometimes precision can be held constant while confidence changes-leading researchers to assume precision and confidence are shaped by different types of information (e.g. perceptual and decisional). To assess this, we examined how visual adaptation to oriented inputs changes tilt perception, perceptual sensitivity and confidence. Some adaptors had a greater detrimental impact on measures of confidence than on precision. We could account for this using an observer model, where precision and confidence rely on different magnitudes of sensory information. These data show that differences in perceptual sensitivity and confidence can therefore emerge, not because these factors rely on different types of information, but because they rely on different magnitudes of sensory information.

Correction to: Predictable events elicit less visual and temporal information uptake in an oddball paradigm.

The Publisher regrets the following production error. The labels for Figures 2, 4, 5, 6, and 7 describe an older version of the figures. The correct figure labels are as follows.

Predictable events elicit less visual and temporal information uptake in an oddball paradigm.

In the visual oddball paradigm, surprising inputs can seem expanded in time relative to unsurprising repeated events. A horizontal input embedded in a train of successive vertical inputs can, for instance, seem relatively protracted in time, even if all inputs are presented for an identical duration. It is unclear if this effect results from surprising events becoming apparently protracted, or from repeated events becoming apparently contracted in time. To disambiguate, we used a non-relative duration reproduction task, in which several standards preceded a test stimulus that had to be reproduced. We manipulated the predictability of test content over successive presentations. Overall, our data suggest that predictable stimuli induce a contraction of apparent duration (Experiments 1, 3, and 4). We also examine sensitivity to test content, and find that predictable stimuli elicit less uptake of visual information (Experiments 2 and 3). We discuss these findings in relation to the predictive coding framework.