Active sampling in visual search is coupled to the cardiac cycle

Recent research has demonstrated that perception and reasoning vary according to the phase of internal bodily signals such as heartbeat. This has been shown by locking the presentation of sensory events to distinct phases of the cardiac cycle. However, task-relevant information is not usually encountered in such a phase-locked manner nor passively accessed, but rather actively sampled at one's own pace. Moreover, if the phase of the cardiac cycle is an important modulator of perception and cognition, as previously proposed, then the way in which we actively sample the world should be similarly modulated by the phase of the cardiac cycle. Here we tested this by coregistration of eye movements and heartbeat signals while participants freely compared differences between two visual arrays. Across three different analyses, we found a significant coupling of saccades, subsequent fixations, and blinks with the cardiac cycle. More eye movements were generated during the systolic phase of the cardiac cycle, which has been reported as the period of maximal effect of the baroreceptors' activity upon cognition. Conversely, more fixations were found during the diastole phase (quiescent baroreceptors). Lastly, more blinks were generated in the later period of the cardiac cycle. These results suggest that interoceptive and exteroceptive processing do adjust to each other; in our case, by sampling the outer environment during quiescent periods of the inner organism

Emotional representations of space vary as a function of peoples' affect and interoceptive sensibility

Most research on people’s representation of space has focused on spatial appraisal and navigation. But there is more to space besides navigation and assessment: people have different emotional experiences at different places, which create emotionally tinged representations of space. Little is known about the emotional representation of space and the factors that shape it. The purpose of this study was to develop a graphic methodology to study the emotional representation of space and some of the environmental features (non-natural vs. natural) and personal features (affective state and interoceptive sensibility) that modulate it. We gave participants blank maps of the region where they lived and asked them to apply shade where they had happy/sad memories, and where they wanted to go after Covid-19 lockdown. Participants also completed self-reports on affective state and interoceptive sensibility. By adapting methods for analyzing neuroimaging data, we examined shaded pixels to quantify where and how strong emotions are represented in space. The results revealed that happy memories were consistently associated with similar spatial locations. Yet, this mapping response varied as a function of participants’ affective state and interoceptive sensibility. Certain regions were associated with happier memories in participants whose affective state was more positive and interoceptive sensibility was higher. The maps of happy memories, desired locations to visit after lockdown, and regions where participants recalled happier memories as a function of positive affect and interoceptive sensibility overlayed significantly with natural environments. These results suggest that people’s emotional representations of their environment are shaped by the naturalness of places, and by their affective state and interoceptive sensibility

Modulation of motor cortex activity in a visual working memory task of hand images

Recent studies suggest that brain regions engaged in perception are also recruited during the consolidation interval of the percept in working memory (WM). Evidence for this comes from studies showing that maintaining arbitrary visual, auditory, and tactile stimuli in WM elicits recruitment of the corresponding sensory cortices. Here we investigate if encoding and WM maintenance of visually perceived body-related stimuli engage just visual regions, or additional sensorimotor regions that are classically associated with embodiment processes in studies of body and action perception. We developed a novel WM paradigm in which participants were asked to remember body and control non-body-related images. In half of the trials, visual-evoked activity that was time-locked to the sight of the stimuli allowed us to examine visual processing of the stimuli to-be-remembered (visual-only trials). In the other half of the trials we additionally elicited a task irrelevant key pressing during the consolidation interval of the stimuli in WM. This manipulation elicited motor-cortical potentials (MCPs) concomitant to visual processing (visual-motor trials). This design allowed us to dissociate motor activity depicted in the MCPs from concurrent visual processing by subtracting activity from the visual-only trials to the compound activity found in the visual-motor trials. After dissociating the MCPs from concomitant visual activity, the results show that only the body-related images elicited neural recruitment of sensorimotor regions over and above visual effects. Importantly, the number of body stimuli to-be-remembered (memory load) modulated this later motor cortical activity. The current observations link together research in embodiment and WM by suggesting that neural recruitment is driven by the nature of the information embedded in the percept

Revealing mnemonic representations of the body in the brain

Current accounts in the memory field suggest that perceptual mechanisms underpin both perception and memory processes. The overlap between perceptual and mnemonic mechanisms has been mainly shown when processing arbitrary stimuli (e.g., shapes and colours). Nevertheless, it still unclear how more socially meaningful stimuli such as others’ bodies are perceived and later maintained in memory. This thesis investigates the encoding and memory maintenance of visually perceived body-related information. Chapter 1 reviews current accounts in the overall memory field. Secondly, it reviews evidence for the presence of a memory system to encode and maintain body-related information in working memory. Chapter 2 describes the EEG technique and proposes a novel method to isolate brain activity arising in sensorimotor cortex from concomitant visual activity that is elicited at the sight of visually perceived body stimuli. Chapter 2.5 outlines how the stimuli for the experiments of this thesis were created. Chapter 3 reports the first study looking into the transformation of visual bodily percepts into mnemonic body representations. This was done by adapting well-known working memory paradigms and the EEG method outlined in Chapter 2. The results showed that holding in memory body-related stimuli involves visual acquisition but quick recoding of the visual input onto somatosensory cortices. Chapter 4 includes another new EEG study that allowed exploration of more anterior brain areas (i.e., motor regions) during memory maintenance of body images in memory. To this end, visual-evoked potentials were combined with motor-cortical potentials. Chapter 5 followed up the two previous EEG studies with three different behavioural versions centred on interfering with the on going processing of body stimuli. Specifically, different forms of sensorimotor suppression were applied during encoding and maintenance of body-related information in memory. Altogether, the 20 methodology and experiments of this PhD work suggest that compared to mnemonic processing of non-body-related images, holding body-related stimuli in memory (beyond the perceptual stage) recruits brain areas such as somatosensory and motor cortices. Finally, Chapter 6 reflects on the results of these studies, offering an overview of this PhD work, as well as on the limitations, technicalities, and potential future studies

Persistent recruitment of somatosensory cortex during active maintenance of hand images in working memory

Working memory (WM) supports temporary maintenance of task-relevant information. This process is associated with persistent activity in the sensory cortex processing the information (e.g., visual stimuli activate visual cortex). However, we argue here that more multifaceted stimuli moderate this sensory-locked activity and recruit distinctive cortices. Specifically, perception of bodies recruits somatosensory cortex (SCx) beyond early visual areas (suggesting embodiment processes). Here we explore persistent activation in processing areas beyond the sensory cortex initially relevant to the modality of the stimuli. Using visual and somatosensory evoked-potentials in a visual WM task, we isolated different levels of visual and somatosensory involvement during encoding of body and non-body-related images. Persistent activity increased in SCx only when maintaining body images in WM, whereas visual/posterior regions' activity increased significantly when maintaining non-body images. Our results bridge WM and embodiment frameworks, supporting a dynamic WM process where the nature of the information summons specific processing resources

People can identify the likely owner of heartbeats by looking at individuals' faces

For more than a century it has been proposed that visceral and vasomotor changes inside the body influence and reflect our experience of the world. For instance, cardiac rhythms (heartbeats and consequent heart rate) reflect psychophysiological processes that underlie our cognition and affective experience. Yet, considering that we usually infer what others do and feel through vision, whether people can identify the most likely owner of a given bodily rhythm by looking at someone's face remains unknown. To address this, we developed a novel two-alternative forced-choice task in which 120 participants watched videos showing two people side by side and visual feedback from one of the individuals' heartbeats in the centre. Participants' task was to select the owner of the depicted heartbeats. Across five experiments, one replication, and supplementary analyses, the results show that: i) humans can judge the most likely owner of a given sequence of heartbeats significantly above chance levels, ii) that performance in such a task decreases when the visual properties of the faces are altered (inverted, masked, static), and iii) that the difference between the heart rates of the individuals portrayed in our 2AFC task seems to contribute to participants' responses. While we did not disambiguate the type of information used by the participants (e.g., knowledge about appearance and health, visual cues from heartbeats), the current work represents the first step to investigate the possible ability to infer or perceive others' cardiac rhythms. Overall, our novel observations and easily adaptable paradigm may generate hypotheses worth examining in the study of human and social cognition

Revealing the body in the brain: an ERP method to examine sensorimotor activity during visual perception of body-related information

Examining the processing of others’ body-related information in the perceivers’ brain across the neurotypical and clinical population is a key topic in the domain of cognitive neurosciences. We argue that beyond classical neuroimaging techniques and frequency analyses, methods that can be easily adapted to capture the fast processing of body-related information in the brain are needed. Here we introduce a novel method that allows this by measuring event-related potentials recorded with electroencephalography (ERPs-EEG). This method possesses known EEG advantages (low cost, high temporal resolution, established paradigms) plus an improvement of its main limitation; i.e., spatiotemporally smoothed resolution due to mixed neural sources. This occurs when participants are presented and process images of bodies/actions that recruit posterior visual cortices. Such stimulus-evoked activity may spread and contaminate the recording of simultaneous activity arising from sensorimotor brain areas, which also process body-related information. Therefore, it is difficult to dissociate the contributing role of different brain regions. To overcome this, we propose eliciting a combination of somatosensory, motor, and visual-evoked potentials during processing of body-related information (vs. non-body-related). Next, brain activity from sensorimotor and visual systems can be dissociated by subtracting activity from trials containing only visual-evoked potentials to those trials containing either a mixture of visual and somatosensory or visual and motor-cortical potentials. This allows isolating visually driven neural activity in areas other than visual. To introduce this method, we revise recent work using this method, consider the processing of body-related stimuli in the brain, as well as outline key methodological aspects to-be-considered. This work provides a clear guideline to researchers interested or transitioning from behavioural to ERPs studies, offering the possibility to adapt well-established paradigms in the EEG realm to study others’ body-related processing in the perceiver’s own cortical body representation (e.g., examining classical EEG components in the social and embodiment frameworks)

Reduced differentiation of emotion-associated bodily sensations in autism

Differences in understanding emotion in autism are well-documented, although far more research has considered how being autistic impacts an understanding of other people’s emotions, compared to their own. In neurotypical adults and children, many emotions are associated with distinct bodily maps of experienced sensation, and the ability to report these maps is significantly related to the awareness of interoceptive signals. Here, in 100 children who either carry a clinical diagnosis of autism (n = 45) or who have no history of autism (n = 55), we investigated potential differences in differentiation across autistic children’s bodily maps of emotion, as well as how such differentiation relates to the processing of interoceptive signals. As such, we measured objective interoceptive performance using the heartbeat-counting task, and participants’ subjective experience of interoceptive signals using the child version of the Body Perception Questionnaire. We found less differentiation in the bodily maps of emotion in autistic children, but no association with either objective or subjective interoceptive processing. These findings suggest that, in addition to previously reported differences in detecting others’ emotional states, autistic children have a less differentiated bodily experience of emotion. This does not, however, relate to differences in interoceptive perception as measured here

Searching for bodies: ERP evidence for independent somatosensory processing during visual search for body-related information

Attention allows us to select relevant information by modulating neural activity within sensory brain areas processing that information. Previous research has shown that visual perception of body stimuli recruits visual cortices together with observer's body representation in somatosensory cortex, which is known for processing body-related information (e.g., haptics, kinematics). However, whether attentional selection of visual body stimuli involves just visual or additional somatosensory areas remains elusive. Here we elicited visual and somatosensory evoked activity during a visual search task, whereby participants searched for target hand images defined by either visual (colour) or bodily (posture) features. In line with previous studies, we found electrophysiological evidence for attentional selection over visual areas (i.e., N2pc) regardless of the feature type. Importantly, after dissociating somatosensory from visual evoked activity, we show that only attentional selection of hand posture - but not hand colour - elicits modulation of somatosensory evoked electrocortical activity over somatosensory cortex. This suggests that attention may not only modulate cortical activity associated with the input-sensory modality (in this case, visual), but, depending on the type of attended information, it may also modulate cortical activity associated with another task-relevant sensory modality (in this case, somatosensory). Overall, our results provide evidence for a flexible attention mechanism that operates according to specific behavioural goals and the information embedded in the percept