Neural and behavioral effects of subordinate-level training of novel objects across manipulations of color and spatial frequency

Bayesian estimation of group event-related potential components (BEGEP): testing a model for synthetic and real datasets

Objective.The spatial resolution of event-related potentials (ERPs) recorded on the head surface is quite low, since the sensors located on the scalp register mixtures of signals from several cortical sources. Bayesian models for multi-channel ERPs obtained from a group of subjects under multiple task conditions can aid in recovering signals from these sources.Approach.This study introduces a novel model that captures several important characteristics of ERP, including person-to-person variability in the magnitude and latency of source signals. Furthermore, the model takes into account that ERP noise, the main source of which is the background electroencephalogram, has the following properties: it is spatially correlated, spatially heterogeneous, and varies over time and from person to person. Bayesian inference algorithms have been developed to estimate the parameters of this model, and their performance has been evaluated through extensive experiments using synthetic data and real ERPs records in a large number of subjects (N= 351).Main results.The signal estimates obtained using these algorithms were compared with the results of the analysis of ERPs by conventional methods. This comparison showed that the use of this model is suitable for the analysis of ERPs and helps to reveal some features of source signals that are difficult to observe in their mixture signals recorded on the scalp.Significance.This study shown that the proposed method is a potentially useful tool for analyzing ERPs collected from groups of subjects in various cognitive neuroscience experiments.

The emergence of the EEG dominant rhythm across the first year of life

The spectral composition of EEG provides important information on the function of the developing brain. For example, the frequency of the dominant rhythm, a salient features of EEG data, increases from infancy to adulthood. Changes of the dominant rhythm during infancy are yet to be fully characterized, in terms of their developmental trajectory and spectral characteristics. In this study, the development of dominant rhythm frequency was examined during a novel sustained attention task across 6-month-old (n = 39), 9-month-old (n = 30), and 12-month-old (n = 28) infants. During this task, computer-generated objects and faces floated down a computer screen for 10 s after a 5-second fixation cross. The peak frequency in the range between 5 and 9 Hz was calculated using center of gravity (CoG) and examined in response to faces and objects. Results indicated that peak frequency increased from 6 to 9 to 12 months of age in face and object conditions. We replicated the same result for the baseline. There was high reliability between the CoGs in the face, object, and baseline conditions across all channels. The developmental increase in CoG was more reliable than measures of mode frequency across different conditions. These findings suggest that CoG is a robust index of brain development across infancy.

A perceptual field test in object experts using gaze-contingent eye tracking

A hallmark of expert object recognition is rapid and accurate subordinate-category recognition of visually homogenous objects. However, the perceptual strategies by which expert recognition is achieved is less known. The current study investigated whether visual expertise changes observers' perceptual field (e.g., their ability to use information away from fixation for recognition) for objects in their domain of expertise, using a gaze-contingent eye-tracking paradigm. In the current study, bird experts and novices were presented with two bird images sequentially, and their task was to determine whether the two images were of the same species (e.g., two different song sparrows) or different species (e.g., song sparrow and chipping sparrow). The first study bird image was presented in full view. The second test bird image was presented fully visible (full-view), restricted to a circular window centered on gaze position (central-view), or restricted to image regions beyond a circular mask centered on gaze position (peripheral-view). While experts and novices did not differ in their eye-movement behavior, experts' performance on the discrimination task for the fastest responses was less impaired than novices in the peripheral-view condition. Thus, the experts used peripheral information to a greater extent than novices, indicating that the experts have a wider perceptual field to support their speeded subordinate recognition.

Using global feedback to induce learning of gist of abnormality in mammograms

Extraction of global structural regularities provides general 'gist' of our everyday visual environment as it does the gist of abnormality for medical experts reviewing medical images. We investigated whether naïve observers could learn this gist of medical abnormality. Fifteen participants completed nine adaptive training sessions viewing four categories of unilateral mammograms: normal, obvious-abnormal, subtle-abnormal, and global signals of abnormality (mammograms with no visible lesions but from breasts contralateral to or years prior to the development of cancer) and receiving only categorical feedback. Performance was tested pre-training, post-training, and after a week's retention on 200 mammograms viewed for 500 ms without feedback. Performance measured as d' was modulated by mammogram category, with the highest performance for mammograms with visible lesions. Post-training, twelve observed showed increased d' for all mammogram categories but a subset of nine, labelled learners also showed a positive correlation of d' across training. Critically, learners learned to detect abnormality in mammograms with only the global signals, but improvements were poorly retained. A state-of-the-art breast cancer classifier detected mammograms with lesions but struggled to detect cancer in mammograms with the global signal of abnormality. The gist of abnormality can be learned through perceptual/incidental learning in mammograms both with and without visible lesions, subject to individual differences. Poor retention suggests perceptual tuning to gist needs maintenance, converging with findings that radiologists' gist performance correlates with the number of cases reviewed per year, not years of experience. The human visual system can tune itself to complex global signals not easily captured by current deep neural networks.

A label isn't just a label: Brief training leads to label-dependent visuo-cortical processing in adults

The current study examines the extent to which hearing individual-level names (e.g., Jimmy) and category-level labels (e.g., Hitchel) paired with novel objects impacts neural responses across a brief (6 min) learning period. Event-related Potentials (ERPs) were recorded while adult participants (n = 44) viewed and heard exemplars of two different species of named novel objects. ERPs were examined for each labeling condition and compared across the first and second half of the learning trials (∼3 min/half). Mean amplitude decreased for the P1 and increased for the N170 from the first to the second half of trials. The decrease in P1 was right lateralized. In addition, the P1 amplitude recorded over right occipitotemporal regions was greater than left occipitotemporal areas, but only for objects paired with individual-level labels. Category-level labels did not show regional P1 differences. The N250 component was greatest over the right occipitotemporal region and was enhanced for objects labeled with individual-level relative to category-level names during the second half of trials. Overall, these findings highlight the unfolding of label-dependent visual processing across a short training period in adults. The results suggest that linguistic labels have an important, top-down impact, on visual processing and that label specificity shapes visuo-cortical responses within a 6-min learning period.

Meaning above (and in) the head: Combinatorial visual morphology from comics and emoji

Compositionality is a primary feature of language, but graphics can also create combinatorial meaning, like with items above faces (e.g., lightbulbs to mean inspiration). We posit that these “upfixes” (i.e., upwards affixes) involve a productive schema enabling both stored and novel face–upfix dyads. In two experiments, participants viewed either conventional (e.g., lightbulb) or unconventional (e.g., clover-leaves) upfixes with faces which either matched (e.g., lightbulb/smile) or mismatched (e.g., lightbulb/frown). In Experiment 1, matching dyads sponsored higher comprehensibility ratings and faster response times, modulated by conventionality. In Experiment 2, event-related brain potentials (ERPs) revealed conventional upfixes, regardless of matching, evoked larger N250s, indicating perceptual expertise, but mismatching and unconventional dyads elicited larger semantic processing costs (N400) than conventional-matching dyads. Yet mismatches evoked a late negativity, suggesting congruent novel dyads remained construable compared with violations. These results support that combinatorial graphics involve a constrained productive schema, similar to the lexicon of language.

The FreqTag toolbox: A principled approach to analyzing electrophysiological time series in frequency tagging paradigms

Steady-state visual evoked potential (ssVEP) frequency tagging is an increasingly used method in electrophysiological studies of visual attention and perception. Frequency tagging is suitable for studies examining a wide range of populations, including infants and children. Frequency tagging involves the presentation of different elements of a visual array at different temporal rates, thus using stimulus timing to “tag” the brain response to a given element by means of a unique time signature. Leveraging the strength of the ssVEP frequency tagging method to isolate brain responses to concurrently presented and spatially overlapping visual objects requires specific signal processing methods. Here, we introduce the FreqTag suite of functions, an open source MATLAB toolbox. The purpose of the FreqTag toolbox is three-fold. First, it will equip users with a set of transparent and reproducible analytical tools for the analysis of ssVEP data. Second, the toolbox is designed to illustrate fundamental features of frequency domain and time-frequency domain approaches. Finally, decision criteria for the application of different functions and analyses are described. To promote reproducibility, raw algorithms are provided in a modular fashion, without additional hidden functions or transformations. This approach is intended to facilitate a fundamental understanding of the transformations and algorithmic steps in FreqTag, and to allow users to visualize and test each step in the toolbox.

Dissociations between performance and visual fixations after subordinate- and basic-level training with novel objects

Previous work suggests that subordinate-level object training improves exemplar-level perceptual discrimination over basic-level training. However, the extent to which visual fixation strategies and the use of visual features, such as color and spatial frequency (SF), change with improved discrimination was not previously known. In the current study, adults (n = 24) completed 6 days of training with 2 families of computer-generated novel objects. Participants were trained to identify one object family at the subordinate level and the other object family at the basic level. Before and after training, discrimination accuracy and visual fixations were measured for trained and untrained exemplars. To examine the impact of training on visual feature use, image color and SF were manipulated and tested before and after training. Discrimination accuracy increased for the object family trained at the subordinate-level, but not for the family trained at the basic level. This increase was seen for all image manipulations (color, SF) and generalized to untrained exemplars within the trained family. Both subordinate- and basic-level training increased average fixation duration and saccadic amplitude and decreased the number of total fixations. Collectively, these results suggest a dissociation between discrimination accuracy, indicative of recognition, and the associated pattern of changes present for visual fixations.