Binocular Rivalry of Emotional Expressions

A central debate in defining emotional space is whether emotions are organized categorically (e.g., fear, happy, disgust) or continuously (i.e., along the independent dimensions of valence and arousal). Emotional facial expressions are one tool often leveraged in trying to define emotional space. Faces are rich sources of social and emotional information. Faces, like emotions, can be organized in either categorical (e.g., happy, sad) or continuous (e.g., open-closed) ways. Therefore, understanding the relatedness of emotional facial expressions to each other may shed light on the underlying structure of emotions. Binocular rivalry (BR) is a tool which can be leveraged to measure the relatedness of two percepts. When each eye is presented with a different image, the visual system is forced to resolve the images into a coherent percept by either selecting one percept to dominate or blending the two images. BR was employed across three experiments with emotional expressions (happy, fear, disgust, sadness, and neutral) to quantify similarities and differences in how the visual system responds to emotional faces. In Study 1, emotional faces dominated over neutral faces. In Study 2, emotion-emotion conflict was explored, and results suggest a positivity bias in emotion perception, as happy faces dominated over all negative faces. In addition, fear dominated over disgust and sad faces. In Study 3, the role of top-down, directed attention on perception was tested by asking participants to direct their attention to the presence or absence of positivity or negativity. Results suggest that the positivity bias observed in Study 2 is enhanced by directed attention towards positivity. Overall, these studies demonstrate that emotion expression information is processed preferentially compared to neutral expressions, that emotion-emotion conflict can be characterized by both positivity and fear biases, and that top-down attention can modulate these biases. Results from these studies were not consistent with any continuous models that were tested. Therefore, results can be interpreted as supporting a categorical emotion model in which happy and fear are prioritized compared to other emotions

The role of frontal cortex in the generation of saccadic eye movements and fixation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1995.Includes bibliographical references (leaves 157-165).by Marc A. Sommer.Ph.D

Role of the primate basal ganglia in saccadic eye movements

The basal ganglia are critical for motor behavior, and a well-known deficit of basal ganglia disorders is the loss of voluntary control over movements. Many studies on the role of basal ganglia in saccadic eye movements have focused on the caudate and substantia nigra pars reticulata (SNr). It has remained unclear, however, whether neurons in other nuclei of the basal ganglia are active during oculomotor behavior and, if they are, whether their activity is preferential for voluntary saccades. We ventured beyond the caudate-SNr pathway to study the globus pallidus externa (GPe) and interna (GPi). First we recorded from neurons in GPe and GPi (and for comparison, in SNr) in monkeys that made memory-guided saccades. Neurons in all three structures had activity synchronized with saccade generation, visual stimulation, or reward. GPe activity was strongly visual-related while GPi activity was more reward-related. The distribution of signals in GPe, but not GPi, resembled that found in SNr. Response fields of neurons in all three structures were more spatially tuned early in trials (during visual and saccadic events) than later in trials (during reward). In our second study, we examined whether saccade-related activity in GPe and GPi was preferentially active for voluntary saccades as defined in two ways: made in the absence of visual stimulation and made in the absence of instructions. We designed tasks that covered all four permutations of presence or absence of visual stimulation and instruction, and analyzed neuronal activity associated with the same vectors of saccades across all the tasks. For about half of the saccade-related neurons in all three structures, saccade-related activity varied with task context. The most prominent factor accounting for differential saccade-related activity was instructional context. Surprisingly, we found higher activity for instructed saccades. Preferential activity for non-instructed (highly voluntary) tasks was rare in individual neurons and absent at the population level.We conclude that GPe and GPi, in addition to SNr, may contribute to oculomotor behavior, and that none of these structures are preferentially active for voluntary saccades. Both of these results provide new views on the role of basal ganglia in eye movements

Chaos in percepts?

Multistability in perceptual tasks has suggested that the mechanisms underlying our percepts might be modeled as nonlinear, deterministic systems that exhibit chaotic behavior. We present evidence supporting this view, obtaining an estimate of 3.5 for the dimensionality of such a system. A surprising result is that this estimate applies for a rather diverse range of perceptual tasks