An exploratory analysis of head-tilting in dogs

Little is known about head-tilts in dogs. Based on previous investigations on the head turning and the lateralised brain pattern of human speech processing in dogs, we hypothesised that head-tilts may be related to increased attention and could be explained by lateralised mental functions. We observed 40 dogs during object-label knowledge tests and analysed head-tilts occurring while listening to humans requesting verbally to fetch a familiar toy. Our results indicate that only dogs that had learned the name of the objects tilted their heads frequently. Besides, the side of the tilt was stable across several months and tests. Thus, we suggest a relationship between head-tilting and processing relevant, meaningful stimuli.

Novelty detection in early olfactory processing of the honey bee, Apis mellifera

Animals are constantly bombarded with stimuli, which presents a fundamental problem of sorting among pervasive uninformative stimuli and novel, possibly meaningful stimuli. We evaluated novelty detection behaviorally in honey bees as they position their antennae differentially in an air stream carrying familiar or novel odors. We then characterized neuronal responses to familiar and novel odors in the first synaptic integration center in the brain, the antennal lobes. We found that the neurons that exhibited stronger initial responses to the odor that was to be familiarized are the same units that later distinguish familiar and novel odors, independently of chemical identities. These units, including both projection neurons and local neurons, showed a decreased response to the familiar odor but an increased response to the novel odor. Our results suggest that the antennal lobe may assign a category of familiarity or novelty to an odor stimulus in addition to its chemical identity code. Therefore, the mechanisms for novelty detection may be present in early sensory processing, either as a result of local synaptic interaction or via feedback from higher brain centers.

Minimal required exposures reveal the primacy of awareness in human face perception

The human visual system is capable of detecting extremely small light signals, as little as one single photon. But what is the visual system's minimal exposure threshold to detect meaningful stimuli? Due to hardware limitations, studies examining fast visual processing typically present stimuli for suprathreshold durations and disrupt processing with a mask. Here, we employed a newly developed tachistoscope that enables sub-millisecond presentations. Combining measures of perceptual sensitivity and recordings of neural activity, we find that both the holistic configuration and the emotional expression of a human face have the same minimal required exposure as the minimal required exposure for faces to reach awareness. These findings indicate that conscious awareness is required for processing meaningful visual information.

More or less of me and you: self-relevance augments the effects of item probability on stimulus prioritization

Self-relevance exerts a powerful influence on information processing. Compared to material associated with other people, personally meaningful stimuli are prioritized during decision-making. Further exploring the character of this effect, here we considered the extent to which stimulus enhancement is impacted by the frequency of self-relevant versus friend-relevant material. In a matching task, participants reported whether shape-label stimulus pairs corresponded to previously learned associations (e.g., triangle = self, square = friend). Crucially however, before the task commenced, stimulus-based expectancies were provided indicating the probability with which both self- and friend-related shapes would be encountered. The results revealed that task performance was impacted by the frequency of stimulus presentation in combination with the personal relevance of the items. When self- and friend-related shapes appeared with equal frequencies, a self-prioritization effect emerged (Expt. 1). Additionally, in both confirmatory (Expt. 2) and dis-confirmatory (Expt. 3) task contexts, stimuli that were encountered frequently (vs. infrequently) were prioritized, an effect that was most pronounced for self-relevant (vs. friend-relevant) items. Further computational analyses indicated that, in each of the reported experiments, differences in performance were underpinned by variation in the rate of information uptake, with evidence extracted more rapidly from self-relevant compared to friend-relevant stimuli. These findings advance our understanding of the emergence and origin of stimulus-prioritization effects during decisional processing.

Overly Strong Priors for Socially Meaningful Visual Signals Are Linked to Psychosis Proneness in Healthy Individuals

According to the predictive coding theory of psychosis, hallucinations and delusions are explained by an overweighing of high-level prior expectations relative to sensory information that leads to false perceptions of meaningful signals. However, it is currently unclear whether the hypothesized overweighing of priors (1) represents a pervasive alteration that extends to the visual modality and (2) takes already effect at early automatic processing stages. Here, we addressed these questions by studying visual perception of socially meaningful stimuli in healthy individuals with varying degrees of psychosis proneness (n = 39). In a first task, we quantified participants’ prior for detecting faces in visual noise using a Bayesian decision model. In a second task, we measured participants’ prior for detecting direct gaze stimuli that were rendered invisible by continuous flash suppression. We found that the prior for detecting faces in noise correlated with hallucination proneness (r = 0.50, p = 0.001, Bayes factor 1/20.1) as well as delusion proneness (r = 0.46, p = 0.003, BF 1/9.4). The prior for detecting invisible direct gaze was significantly associated with hallucination proneness (r = 0.43, p = 0.009, BF 1/3.8) but not conclusively with delusion proneness (r = 0.30, p = 0.079, BF 1.7). Our results provide evidence for the idea that overly strong high-level priors for automatically detecting socially meaningful stimuli might constitute a processing alteration in psychosis.

Greater Visual Working Memory Capacity for Visually Matched Stimuli When They Are Perceived as Meaningful

Almost all models of visual working memory—the cognitive system that holds visual information in an active state—assume it has a fixed capacity: Some models propose a limit of three to four objects, where others propose there is a fixed pool of resources for each basic visual feature. Recent findings, however, suggest that memory performance is improved for real-world objects. What supports these increases in capacity? Here, we test whether the meaningfulness of a stimulus alone influences working memory capacity while controlling for visual complexity and directly assessing the active component of working memory using EEG. Participants remembered ambiguous stimuli that could either be perceived as a face or as meaningless shapes. Participants had higher performance and increased neural delay activity when the memory display consisted of more meaningful stimuli. Critically, by asking participants whether they perceived the stimuli as a face or not, we also show that these increases in visual working memory capacity and recruitment of additional neural resources are because of the subjective perception of the stimulus and thus cannot be driven by physical properties of the stimulus. Broadly, this suggests that the capacity for active storage in visual working memory is not fixed but that more meaningful stimuli recruit additional working memory resources, allowing them to be better remembered.

STUDY OF UNILATERAL SPATIAL NEGLECT IN PARKINSON'S PATIENTS

In Africa, few studies are interested in unilateral spatial neglect (NSU) in Parkinson's disease. However, this syndrome is a deficit to detect, respond to or orientate towards meaningful stimuli (Heil- man, KM 1973), observable after an injury affecting the non-dominant hemisphere for language. The significant handicap it entails justifies the need for early diagnosis and care. The NSU study is mo- tivated by its link with neurocognitive phenomena that are important on the theoretical level (attention, visuospatial and perceptual awareness). The objective is to study USN in Parkinson's pa tients, followed and hospitalized at the Neurology Department of Hassan II University Hospital in Fez. The visual-graphic test that has been used to detect this pathology is that of Bell's test. The test focuses on the detection of targets placed among several stimuli on a sheet of A4 paper. The material included 120 people: 60 Parkinsonian patients: 34 men (56,7%), and 26 women (43,3%) and 60 control subjects: 34 men (56,7%), and 26 women (43,3%). The groups were matched by age and sex. Different aspects of neglect have been observed throughout the Bell's test. It was found that total omission of bell figures was significantly influenced by age, being less frequent in the 35-49 age group in both groups, and higher in the elderly (50-80 years), as well the level of education. It have been reduced considerably with the increase in education. The hand used and the laterality had no effect; t = 3.76 degrees of freedom (df) = 108.27 and p = 0.000. Unilateral spatial neglect has a negative effect in subjects with Parkin- son's disease. It deserves to be systematically sought for a better clinical evaluation and therapeutic management of the patients.

Failure to Report the Identity of a Face that was Just Selected: Attribute Amnesia of Faces

Attribute amnesia (AA) describes a phenomenon in which participants are unable to report an attribute that was just attended to select a target. Most studies investigating this effect used simple stimuli like letters and digits. The few studies using meaningful stimuli, however, found AA only when the target stimuli were used repeatedly. We tested the robustness of this boundary condition with a set of artificially generated faces. Participants were instructed to find the young face among 3 older faces and performed this task for the first 27 trials. On the 28th trial, they were unexpectedly asked to report the identity of the young target face they just saw. The following 4 trials repeated this identity question and the target faces never repeated throughout the experiment. Contrary to the previous findings, we observed AA with the current set of meaningful and unique targets. I.e., The pre-surprise location task performance was at ceiling, but the surprise identity accuracy was significantly lower than the following trial. The current finding expands the boundary conditions of AA and suggests that AA is applicable to visual experience that resembles our day-to-day lives.