On the Mathematical Foundations of Colorimetry: Color-matching, Object Colors and Optimal Colors

The psychophysical description of one of the pillars of color science, the color-matching paradigm, forms the basis of the representation theory of colors. This description entails the weighted integration of a spectral distribution of radiant energy (i.e. a light-ray; ‘stimulus side’) with three color-matching functions (‘observer side’). Here these color-matching functions are conceptualized as a vector-valued measure , which grounds the representation theory of colors in the mathematical frameworks of measure theory and functional analysis. Properties like the convexity and compactness of the tristimulus space and the chromaticity diagram follow readily from this color-matching measure model. Notably also is that within the model metameric colors naturally correspond to -equivalence classes of spectral distributions. Subsequently, an extension of the model is provided for object colors. Among other things, this results in a clear and practical mathematical expression about optimal colors.

Two Distinct Systems Represent Contralateral and Ipsilateral Sensorimotor Processes in the Human Premotor Cortex: A Dense TMS Mapping Study

Animal brains contain behaviorally committed representations of the surrounding world, which integrate sensory and motor information. In primates, sensorimotor mechanisms reside in part in the premotor cortex (PM), where sensorimotor neurons are topographically clustered according to functional specialization. Detailed functional cartography of the human PM is still under investigation. We explored the topographic distribution of spatially dependent sensorimotor functions in healthy volunteers performing left or right, hand or foot, responses to visual cues presented in the left or right hemispace, thus combining independently stimulus side, effector side, and effector type. Event-related transcranial magnetic stimulation was applied to single spots of a dense grid of 10 points on the participants’ left hemiscalp, covering the whole PM. Results showed: (1) spatially segregated hand and foot representations, (2) focal representations of contralateral cues and movements in the dorsal PM, and (3) distributed representations of ipsilateral cues and movements in the ventral and dorso-medial PM. The present novel causal information indicates that (1) the human PM is somatotopically organized and (2) the left PM contains sensory-motor representations of both hemispaces and of both hemibodies, but the hemispace and hemibody contralateral to the PM are mapped on a distinct, nonoverlapping cortical region compared to the ipsilateral ones.

Neural correlates of side-specific odour memory in mushroom body output neurons

Humans and other mammals as well as honeybees learn a unilateral association between an olfactory stimulus presented to one side and a reward. In all of them, the learned association can be behaviourally retrieved via contralateral stimulation, suggesting inter-hemispheric communication. However, the underlying neuronal circuits are largely unknown and neural correlates of across-brain-side plasticity have yet not been demonstrated. We report neural plasticity that reflects lateral integration after side-specific odour reward conditioning. Mushroom body output neurons that did not respond initially to contralateral olfactory stimulation developed a unique and stable representation of the rewarded compound stimulus (side and odour) predicting its value during memory retention. The encoding of the reward-associated compound stimulus is delayed by about 40 ms compared with unrewarded neural activity, indicating an increased computation time for the read-out after lateral integration.

Laboratory Studies of Psychological Stress

This paper reviews current methods of studying psychological stress in contrived settings. Stress may be operationally defined in terms of stimuli, responses or both. On the stimulus side, types of stressors are classified on the basis of stimulus characteristics or kinds of threat involved. On the response side, various indicators of stress are discussed including measures of changes in affective state, adaptive functioning and physiological arousal.

Paired-Associate Learning and Free Recall of Nouns as a Function of Concreteness, Specificity, Imagery, and Meaningfulness

Abstractness-concreteness and generality-specificity of words were simultaneously varied in a factorial design on the stimulus and response sides of paired-associate lists constructed from 96 nouns. The analysis of recall scores from the auditory presentation of 2 alternating study trials and recall trials revealed significant ( p < .001) effects of both variables on the stimulus side of pairs. A smaller effect on the response side was significant ( p < .05) only in the case of specificity. A second experiment showed positive effects ( p < .001) of both concreteness and specificity on free recall. Mean scores were also available for the nouns on their rated capacity to evoke sensory images ( I) and on their meaningfulness ( m). A correlational analysis indicated that, of the attributes involved, I correlated most highly with learning scores. Furthermore, consistent with the hypothesis that stimulus-evoked imagery can mediate response recall, the superiority of I was greatest when the items served as stimulus terms in PA learning.

Temporal Relations and Meaningfulness in Paired-Associate Learning

Each of 34 Ss was presented with a list of 12 paired associates which were arranged according to high-low or low-high stimulus and response meaningfulness and also in a simultaneous or sequential time relationship. Meaningfulness level on the stimulus side of the dyad rather than on the response side was found to be more crucial for learning, and significantly more learning occurred also when the dyads were presented in the simultaneous condition. The findings were discussed in terms of both association theory and the differences between the present procedure and the conventional anticipation method.