Are Electrode Caps Worth the Investment? An Evaluation of EEG Methods in Undergraduate Neuroscience Laboratory Courses and Research.

Electroencephalography (EEG) is a common neuroscience technique that is more accessible to undergraduate programs than expensive techniques such as fMRI and single-cell recording. The use of EEG can provide undergraduates with firsthand neuroscience research experience without taking too many financial resources away from a program. There are multiple types of EEG equipment that can be used, including individual electrodes and electrode caps. This study used surveys administered to students who were in a neuroscience laboratory course, conducting research, or participating in research in order to discern which of these two EEG setups is preferred by undergraduates. According to average reaction scores calculated from the surveys, laboratory students tended to prefer individual electrodes over electrode caps, and when explicitly asked about their overall preference, a majority of laboratory students chose individual electrodes over electrode caps. Additionally, comparable levels of improvement in learning objectives and the quality of data collected in laboratory sessions were found across methods. Student researchers' ratings revealed a marginal preference for caps over individual electrodes, and all 5 researchers surveyed chose caps on a discriminate choice question. Research participants' ratings of caps and individual electrodes, however, were not significantly different. These results do not point to a concrete recommendation of one setup over the other but rather suggest that either setup could be a viable option. Therefore, we conclude that programs can comfortably decide which to use based on their own needs and resources as well as the relative advantages and disadvantages of each setup. For example, individual electrodes may be better for programs with low budgets looking to introduce students to EEG data recording, whereas electrode caps may be better for programs looking to better prepare students for future EEG research or to perform multichannel recordings.

Position selectivity in face-sensitive visual cortex to facial and nonfacial stimuli: an fMRI study.

BACKGROUND: Evidence for position sensitivity in object-selective visual areas has been building. On one hand, most of the relevant studies have utilized stimuli for which the areas are optimally selective and examine small sections of cortex. On the other hand, visual field maps established with nonspecific stimuli have been found in increasingly large areas of visual cortex, though generally not in areas primarily responsive to faces. METHODS: fMRI was used to study the position sensitivity of the occipital face area (OFA) and the fusiform face area (FFA) to both standard rotating wedge retinotopic mapping stimuli and quadrant presentations of synthetic facial stimuli. Analysis methods utilized were both typical, that is, mean univariate BOLD signals and multivoxel pattern analysis (MVPA), and novel, that is, distribution of voxels to pattern classifiers and use of responses to nonfacial retinotopic mapping stimuli to classify responses to facial stimuli. RESULTS: Polar angle sensitivity was exhibited to standard retinotopic mapping stimuli with a stronger contralateral bias in OFA than in FFA, a stronger bias toward the vertical meridian in FFA than in OFA, and a bias across both areas toward the inferior visual field. Contralateral hemispheric lateralization of both areas was again shown using synthetic face stimuli based on univariate BOLD signals, MVPA, and the biased contribution of voxels toward multivariate classifiers discriminating the contralateral visual field. Classifiers based on polar angle responsivity were used to classify the patterns of activation above chance levels to face stimuli in the OFA but not in the FFA. CONCLUSIONS: Both the OFA and FFA exhibit quadrant sensitivity to face stimuli, though the OFA exhibits greater position responsivity across stimuli than the FFA and includes overlap in the response pattern to the disparate stimulus types. Such biases are consistent with varying position sensitivity along different surfaces of occipito-temporal cortex.

A Series of Computational Neuroscience Labs Increases Comfort with MATLAB.

Computational simulations allow for a low-cost, reliable means to demonstrate complex and often times inaccessible concepts to undergraduates. However, students without prior computer programming training may find working with code-based simulations to be intimidating and distracting. A series of computational neuroscience labs involving the Hodgkin-Huxley equations, an Integrate-and-Fire model, and a Hopfield Memory network were used in an undergraduate neuroscience laboratory component of an introductory level course. Using short focused surveys before and after each lab, student comfort levels were shown to increase drastically from a majority of students being uncomfortable or with neutral feelings about working in the MATLAB environment to a vast majority of students being comfortable working in the environment. Though change was reported within each lab, a series of labs was necessary in order to establish a lasting high level of comfort. Comfort working with code is important as a first step in acquiring computational skills that are required to address many questions within neuroscience.

The perception of object versus objectless motion.

Wertheimer, M. (Zeitschrift für Psychologie und Physiologie der Sinnesorgane, 61:161-265, 1912) classical distinction between beta (object) and phi (objectless) motion is elaborated here in a series of experiments concerning competition between two qualitatively different motion percepts, induced by sequential changes in luminance for two-dimensional geometric objects composed of rectangular surfaces. One of these percepts is of spreading-luminance motion that continuously sweeps across the entire object; it exhibits shape invariance and is perceived most strongly for fast speeds. Significantly for the characterization of phi as objectless motion, the spreading luminance does not involve surface boundaries or any other feature; the percept is driven solely by spatiotemporal changes in luminance. Alternatively, and for relatively slow speeds, a discrete series of edge motions can be perceived in the direction opposite to spreading-luminance motion. Akin to beta motion, the edges appear to move through intermediate positions within the object's changing surfaces. Significantly for the characterization of beta as object motion, edge motion exhibits shape dependence and is based on the detection of oppositely signed changes in contrast (i.e., counterchange) for features essential to the determination of an object's shape, the boundaries separating its surfaces. These results are consistent with area MT neurons that differ with respect to speed preference Newsome et al (Journal of Neurophysiology, 55:1340-1351, 1986) and shape dependence Zeki (Journal of Physiology, 236:549-573, 1974).

Changes in pupil diameter entrained by cortically initiated changes in attention.

The diameter of the pupil is affected by changes in ambient illumination, color, spatial structure, movement, and mental effort. It has now been found that pupil diameter can be affected by cognitive processes. That is, it can be entrained by alternations between broadly spread and narrowly focused attention that are cued exogenously (attention is "summoned" by the cue) or endogenously (attention changes under the perceiver's intentional control). Pupil diameter also is affected by post-eye-blink constrictions that occur most often when attention is narrowed, and possibly by changes evoked by the near reflex, although changes in attention state parsimoniously account for the entirety of the results. Changes in pupil diameter produce differences in spherical aberration that alternately blur (when the pupil dilates) and sharpen the retinal image (when the pupil constricts), affecting the relative sensitivity of large receptive fields that mediate broadly spread attention compared with smaller receptive fields that mediate more narrowly focused attention. Results for endogenously cued, intentional changes in attentional spread provide definitive behavioral evidence for cortical feedback to subcortical nuclei that control pupil diameter, either directly or through pupil-constricting eye blinks. Analyses of convergent and divergent changes in eye position indicate that the near reflex was activated long after the initiation of relatively gradual attentionally cued changes in pupil diameter, and further, that when it occurs, the near reflex facilitates ongoing changes in pupil diameter.

Motion perception induced by dynamic grouping: a probe for the compositional structure of objects.

A new method is described for determining how the visual system resolves ambiguities in the compositional structure of multi-surface objects; i.e., how the surfaces of objects are grouped together to form a hierarchical structure. The method entails dynamic grouping motion, a high level process in which changes in a surface (e.g., increases or decreases in its luminance, hue or texture) transiently perturb its affinity with adjacent surfaces. Affinity is determined by the combined effects of Gestalt and other grouping variables in indicating that a pair of surfaces forms a subunit within an object's compositional structure. Such pre-perturbation surface groupings are indicated by the perception of characteristic motions across the changing surface. When the affinity of adjacent surfaces is increased by a dynamic grouping variable, their grouping is transiently strengthened; the perceived motion is away from their boundary. When the affinity of adjacent surfaces is decreased, their grouping is transiently weakened; the perceived motion is toward the surfaces' boundary. It is shown that the affinity of adjacent surfaces depends on the nonlinear, super-additive combination of affinity values ascribable to individual grouping variables, and the effect of dynamic grouping variables on motion perception depends on the prior, pre-perturbation affinity state of the surfaces. It is proposed that affinity-based grouping of an object's surfaces must be consistent with the activation of primitive three-dimensional object components in order for the object to be recognized. Also discussed is the potential use of dynamic grouping for determining the compositional structure of multi-object scenes.

The line motion illusion: the detection of counterchanging edge and surface contrast.

A version of the line motion illusion (LMI) occurs when one of two adjacent surfaces changes in luminance; a new surface is perceived sliding in front of the initially presented surface. Previous research has implicated high-level mechanisms that can create or modulate LMI motion via feedback to lower-level motion detectors. It is shown here that there also is a non-motion-energy, feedforward basis for LMI motion entailing the detection of counterchange, a spatial pattern of motion-specifying stimulus information that combines changes in edge contrast with oppositely signed changes in background-relative surface contrast. It was concluded that (1) in addition to LMI motion, edge/surface counterchange could be the basis for perceiving continuous object motion, (2) counterchange detection is the likely basis for third-order motion perception (Lu & Sperling, 1995a), and (3) motion energy and counterchange mechanisms could be composed of different arrangements of the same spatial and temporal filters, the former detecting motion at a single location, the latter detecting the motion path between pairs of locations.

Decoding of faces and face components in face-sensitive human visual cortex.

A great challenge to the field of visual neuroscience is to understand how faces are encoded and represented within the human brain. Here we show evidence from functional magnetic resonance imaging (fMRI) for spatially distributed processing of the whole face and its components in face-sensitive human visual cortex. We used multi-class linear pattern classifiers constructed with a leave-one-scan-out verification procedure to discriminate brain activation patterns elicited by whole faces, the internal features alone, and the external head outline alone. Furthermore, our results suggest that whole faces are represented disproportionately in the fusiform cortex (FFA) whereas the building blocks of faces are represented disproportionately in occipitotemporal cortex (OFA). Faces and face components may therefore be organized with functional clustering within both the FFA and OFA, but with specialization for face components in the OFA and the whole face in the FFA.

Stimulus specificity in spatially-extended interocular suppression.

In typical binocular rivalry demonstrations, disparate images presented in corresponding locations to the two eyes are found to alternate perceptually over time. Alternation in perception can occur even if the images presented to the two eyes do not overlap, if they are sufficiently close in space. This implies a spatial spread in the interocular interaction. The current set of experiments explores how the luminance pattern of a target, in relation to a rivalrous suppressor, affects its susceptibility to suppression. It was found that the susceptibility to suppression of a target pattern was nonlinearly related to the amount of luminance variation along the target in the direction perpendicular to the suppressing stimulus. For instance, there was a strong effect of the orientation of the grating pattern within the target on the total time of suppression, with much more suppression for horizontal gratings than vertical gratings when suppressor bars were oriented vertically, regardless of the luminance pattern within the suppressors. Furthermore, it was shown that the inclusion of a spatial gap between the vertical suppressors and the central portion of the target does more than simply change the spatial relationships, it adds new figural information, such as vertically orientated edges in the targets, that modify the susceptibility to suppression of the target, thereby interfering with measurements of spatial interaction functions. All of the results are consistent with selectively suppressing stimulus information that would interfere with stereoscopic matching to aid the binocular fusion of disparate retinal images.

Effect of transient versus sustained activation on interocular suppression.

Switches in perceptual dominance resulting from either binocular rivalry or flash suppression likely involve some mechanism of interocular suppression, although it is unclear from past research whether different mechanisms are involved in the two cases. Using monocular, centrally fixated sinusoidal gratings surrounded by contiguous annuli of rivalrous gratings, suppression of the entire central grating was possible using either technique. However, the magnitude of the suppression was unaffected by the presence of an ipsilateral surround for flash suppression, yet, for binocular rivalry, suppression no longer occurred when the surrounds were fusible. Nevertheless, computational modeling demonstrates that the differences between the techniques may be attributable to the sustained versus transient stimulation of the contralateral surround, with the magnitude of the suppression proportional to the activation of the contralateral surround. Consistent with this, suppression extends over a greater distance at the onset of the contralateral surround than during sustained rivalry. Therefore, it is likely that perceptual dominance in both binocular rivalry and flash suppression is based on the same mechanism of interocular suppression.

Linking dynamical perceptual decisions at different levels of description in motion pattern formation: computational simulations.

A two-level dynamical model of motion pattern formation is developed in which local motion/ nonmotion perceptual decisions are based on inhibitory competition between area V1 detectors responsive to motion-specifying versus motion-independent stimulus information, and pattern-level perceptual decisions are based on inhibitory competition between area MT motion detectors with orthogonal directional selectivity. The model accounts for the effects of luminance perturbations on the relative size of the pattern-level hysteresis effects reported by Hock and Ploeger (2006) and also accounts for related experimental results reported by Hock, Kelso, and Schöner (1993). Single-trial simulations demonstrated the crucial role of local motion/nonmotion bistability and activation-dependent future-shaping interactions in stabilizing perceived global motion patterns. Such interactions maintain currently perceived motion patterns by inhibiting the soon-to-be-stimulated motion detectors that otherwise would be the basis for the perception of an alternative pattern.

Dynamical vs. judgmental comparison: hysteresis effects in motion perception.

Perceptual comparison was investigated by gradually varying the relative length of two apparent motion paths, and independently determining when an initial percept was lost during the course of attribute change and when an alternative percept emerged. Dynamical comparison was indicated by a range of attribute values for which perception was bistable. Within this range, a percept that lost stability was immediately replaced by an alternative percept. Judgmental comparison was indicated by a range of attribute values for which perception was uncertain. When an initial percept was lost, an alternative percept did not immediately emerge because the alternatives being compared could not be distinguished. Differences in the effects of random noise on dynamical vs. judgmental comparison were demonstrated with computational simulations, and implications are discussed for motion energy models and solutions to the motion correspondence problem.

When motion is not perceived: evidence from adaptation and dynamical stability.

Adaptation was used to probe the perceiver's activation state when either motion or nonmotion percepts are formed for bistable, single-element apparent motion stimuli. Although adaptation was not observed in every instance, when it was observed its effect was to increase the probability of both motion-to-nonmotion and nonmotion-to-motion switches, the time scale of adaptation corresponding to neurophysiological observations for directionally selective cortical cells (Giaschi et al. 1993). This susceptibility to de-stabilizing adaptation effects indicated that the nonmotion percept was not the result of inadequate stimulation producing subthreshold levels of motion detector activation; if that were the case, activation-dependent adaptation would have decreased the nonmotion-to-motion switching rate by reducing activation further below threshold. Above-threshold activation levels are therefore associated with both nonmotion and motion perceptual states, and the failure to perceive motion despite the presence of adequate motion detector stimulation can be attributed to inhibitory competition between detectors activated by motion-specifying stimulus information and detectors activated to similar levels by motion-independent stimulus information, consistent with the dynamical quality of single-element apparent motion.