Amanda K. Robinson

Odors enhance the salience of matching images during the attentional blink

As any food critic knows, the visual presentation of a dish can enhance its aroma. Is the reverse also true? Here we investigated whether odors can enhance the salience of familiar visual objects at the limits of perceptual discrimination, using rapid serial visual presentations (RSVP) to induce an attentional blink (AB). We had participants view RSVP streams containing photographs of odor-related objects (lemon, orange, rose, and mint) amongst non-odor related distractors. In each trial, participants inhaled a single odor, which either matched the odor-related target within the stream (congruent trials), did not match the odor-related target (incongruent trials), or was irrelevant with respect to the target. Congruent odors significantly attenuated the AB for odor-related visual targets, compared with incongruent and irrelevant odors. The findings suggest that familiar odors can render matching visual objects more salient, thereby enhancing their competitive strength at the limits of temporal attention.

Olfaction modulates early neural responses to matching visual objects

Sensory information is initially registered within anatomically and functionally segregated brain networks but is also integrated across modalities in higher cortical areas. Although considerable research has focused on uncovering the neural correlates of multisensory integration for the modalities of vision, audition, and touch, much less attention has been devoted to understanding interactions between vision and olfaction in humans. In this study, we asked how odors affect neural activity evoked by images of familiar visual objects associated with characteristic smells. We employed scalp-recorded EEG to measure visual ERPs evoked by briefly presented pictures of familiar objects, such as an orange, mint leaves, or a rose. During presentation of each visual stimulus, participants inhaled either a matching odor, a nonmatching odor, or plain air. The N1 component of the visual ERP was significantly enhanced for matching odors in women, but not in men. This is consistent with evidence that women are superior in detecting, discriminating, and identifying odors and that they have a higher gray matter concentration in olfactory areas of the OFC. We conclude that early visual processing is influenced by olfactory cues because of associations between odors and the objects that emit them, and that these associations are stronger in women than in men.

Very high density EEG elucidates spatiotemporal aspects of early visual processing

Standard human EEG systems based on spatial Nyquist estimates suggest that 20–30 mm electrode spacing suffices to capture neural signals on the scalp, but recent studies posit that increasing sensor density can provide higher resolution neural information. Here, we compared “super-Nyquist” density EEG (“SND”) with Nyquist density (“ND”) arrays for assessing the spatiotemporal aspects of early visual processing. EEG was measured from 128 electrodes arranged over occipitotemporal brain regions (14 mm spacing) while participants viewed flickering checkerboard stimuli. Analyses compared SND with ND-equivalent subsets of the same electrodes. Frequency-tagged stimuli were classified more accurately with SND than ND arrays in both the time and the frequency domains. Representational similarity analysis revealed that a computational model of V1 correlated more highly with the SND than the ND array. Overall, SND EEG captured more neural information from visual cortex, arguing for increased development of this approach in basic and translational neuroscience.

Word and face processing engage overlapping distributed networks: Evidence from RSVP and EEG investigations.

Words and faces have vastly different visual properties, but increasing evidence suggests that word and face processing engage overlapping distributed networks. For instance, fMRI studies have shown overlapping activity for face and word processing in the fusiform gyrus despite well-characterized lateralization of these objects to the left and right hemispheres, respectively. To investigate whether face and word perception influences perception of the other stimulus class and elucidate the mechanisms underlying such interactions, we presented images using rapid serial visual presentations. Across 3 experiments, participants discriminated 2 face, word, and glasses targets (T1 and T2) embedded in a stream of images. As expected, T2 discrimination was impaired when it followed T1 by 200 to 300 ms relative to longer intertarget lags, the so-called attentional blink. Interestingly, T2 discrimination accuracy was significantly reduced at short intertarget lags when a face was followed by a word (face–word) compared with glasses–word and word–word combinations, indicating that face processing interfered with word perception. The reverse effect was not observed; that is, word–face performance was no different than the other object combinations. EEG results indicated the left N170 to T1 was correlated with the word decrement for face–word trials, but not for other object combinations. Taken together, the results suggest face processing interferes with word processing, providing evidence for overlapping neural mechanisms of these 2 object types. Furthermore, asymmetrical face–word interference points to greater overlap of face and word representations in the left than the right hemisphere.

Containing errors in computations for neural sensing: Does a hierarchical-referencing strategy lead to energy savings?

Recent experimental evidence and theoretical results challenge the belief that ultra high-density EEG sensing will not yield higher spatial resolutions. It raises the exciting possibility that source-localization accuracy can be improved substantially with ultra high-density systems; however, these systems are hindered by implementation constraints in circuit volume and energy consumption. Recently, an information-theoretic hierarchical referencing mechanism has been proposed to exploit the decay of high-spatial frequencies during volume conduction from source to scalp — and the induced high local spatial correlations — to reduce the required circuit power and volume. In this paper, human EEG data is used to experimentally test and validate theoretical inter-electrode correlations and bit savings when employing a hierarchical referencing strategy. Extrapolating from electrodes that are at least 2 cm apart, we observe that on average savings can exceed 3 bits per electrode at inter-electrode distances of 3 mm.

Odours reduce the magnitude of object substitution masking for matching visual targets in females.

Recent evidence suggests that olfactory stimuli can influence early stages of visual processing, but there has been little focus on whether such olfactory-visual interactions convey an advantage in visual object identification. Moreover, despite evidence that some aspects of olfactory perception are superior in females than males, no study to date has examined whether olfactory influences on vision are gender-dependent. We asked whether inhalation of familiar odorants can modulate participants’ ability to identify briefly flashed images of matching visual objects under conditions of object substitution masking (OSM). Across two experiments, we had male and female participants (N = 36 in each group) identify masked visual images of odour-related objects (e.g., orange, rose, mint) amongst nonodour-related distracters (e.g., box, watch). In each trial, participants inhaled a single odour that either matched or mismatched the masked, odour-related target. Target detection performance was analysed using a signal detection (d’) approach. In females, but not males, matching odours significantly reduced OSM relative to mismatching odours, suggesting that familiar odours can enhance the salience of briefly presented visual objects. We conclude that olfactory cues exert a subtle influence on visual processes by transiently enhancing the salience of matching object representations. The results add to a growing body of literature that points towards consistent gender differences in olfactory perception.

Distinct neural processes for the perception of familiar versus unfamiliar faces along the visual hierarchy revealed by EEG

ABSTRACT Humans recognize faces with ease, despite the complexity of the task and of the visual system which underlies it. Different spatial regions, including both the core and extended face processing networks, and distinct temporal stages of processing have been implicated in face recognition, but there is ongoing controversy regarding the extent to which the mechanisms for recognizing a familiar face differ from those for an unfamiliar face. Here, we used electroencephalogram (EEG) and flicker SSVEP, a high signal‐to‐noise approach, and searchlight decoding methods to elucidate the mechanisms mediating the processing of familiar and unfamiliar faces in the time domain. Familiar and unfamiliar faces were presented periodically at 15Hz, 6Hz and 3.75Hz either upright or inverted in separate blocks, with the rationale that faster frequencies require shorter processing times per image and tap into fundamentally different levels of visual processing. The 15Hz trials, likely to reflect early visual processing, exhibited enhanced neural responses for familiar over unfamiliar face trials, but only when the faces were upright. In contrast, decoding methods revealed similar classification accuracies for upright and inverted faces for both familiar and unfamiliar faces. For the 6Hz frequency, familiar faces had lower amplitude responses than unfamiliar faces, and decoding familiarity was more accurate for upright compared with inverted faces. Finally, the 3.75Hz frequency revealed no main effects of familiarity, but decoding showed significant correlations with behavioral ratings of face familiarity, suggesting that activity evoked by this slow presentation frequency reflected higher‐level, cognitive aspects of familiarity processing. This three‐way dissociation between frequencies reveals that fundamentally different stages of the visual hierarchy are modulated by face familiarity. The combination of experimental and analytical approaches used here represent a novel method for elucidating spatio‐temporal characteristics within the visual system.

Challenges and Opportunities in Instrumentation and Use of High-Density EEG for Underserved Regions

Electroencephalography (EEG) is a non-invasive method of measuring electrical signals from the brain. However, traditional clinical EEG uses only 10–40 electrodes for diagnosis which limits its potential as an imaging modality. High-density (HD) EEG, as well as the more recent Ultra-High-Density (UHD) EEG, are imaging platforms that can be used to image the brain using various techniques to solve inverse problems. These platforms comprise a measurement device and algorithms for data analysis. Recent studies have provided promising evidence that increasing the density of electrodes can improve resolution up to at least approximately 1,000 electrodes for whole-scalp coverage. Both HD and UHD-EEG can be made inexpensive and portable; therefore, perhaps most importantly, accessible to many parts of the world. However, there are remaining challenges that can hinder HD- and UHD-EEG development and use. Here, we discuss these challenges and present the approaches our research program has developed to overcome them.

Odours modulate early neural responses to matching visual objects

Sensory information is initially registered within anatomically and functionally segregated brain networks, but is also integrated across modalities in higher cortical areas. Although considerable research has focused on uncovering the neural correlates of multisensory integration for the modalities of vision and audition, much less effort has been devoted to understanding interactions between vision and olfaction. Here we asked whether odours affect neural activity evoked by images of familiar visual objects that carry characteristic smells (e.g., orange, mint, rose). We employed scalp-recorded electroencephalography to measure visual event-related potentials (ERPs) to briefly presented photographs of familiar, odour-related objects, such as an orange or mint leaves. On each trial, participants ( N = 26 ) inhaled either a matching odour (e.g., orange scent for a photograph of an orange fruit), a non-matching odour (e.g., mint scent for a photograph of an orange fruit), an irrelevant odour (coffee), or plain air. Participants maintained their attention on the visual stimuli by judging the shape of a border surrounding each picture. The N1 component of the visual ERP, 100–170 ms after image presentation, was reliably enhanced for matching odours in female participants, but not in males. This is consistent with evidence that females are superior in detecting, discriminating and identifying odours, and that they have a higher grey matter concentration in olfactory areas of the orbitofrontal cortex. We conclude that early visual processing is influenced by olfaction due to learned associations between odours and the objects that emit them, and that these associations are stronger in females than males.