The reconstruction of the perceptual spaces of brightness and color on the basis of visual evoked potentials and their comparison with the data from behavioral trials

The visual evoked potentials to a change in color stimuli were studied. The amplitude of the N85 component was correlated with color discrimination. In cases when the brightness of one color was fixed and that of the other one changed, the amplitude dynamics of N85 was V-shaped with the minimum corresponding to the point of equal brightness of both colors. The N85 amplitude in this point serves as a measure of discrimination between stimuli chromaticity. The perceptual color space in rabbit (possessing two cone pigments) was constructed in accordance with the amplitudes of N85 to color change. This space represented a hypersphere in the four-dimensional Euclidean space. The perceptual spaces for brightness and color reconstructed on the basis of conditioning probabilities and N85 amplitudes evoked by replacement of colored and achromatic stimuli were shown to coincide. This suggests the common mechanism of the vector color coding.     

Memory Color Effect Induced by Familiarity of Brand Logos

Background

When people are asked to adjust the color of familiar objects such as fruits until they appear achromatic, the subjective gray points of the objects are shifted away from the physical gray points in a direction opposite to the memory color (memory color effect). It is still unclear whether the discrepancy between memorized and actual colors of objects is dependent on the familiarity of the objects. Here, we conducted two experiments in order to examine the relationship between the degree of a subject’s familiarity with objects and the degree of the memory color effect by using logographs of food and beverage companies.

Methods and Findings

In Experiment 1, we measured the memory color effects of logos which varied in terms of their familiarity (high, middle, or low). Results demonstrate that the memory color effect occurs only in the high-familiarity condition, but not in the middle- and low-familiarity conditions. Furthermore, there is a positive correlation between the memory color effect and the actual number of domestic stores of the brand. In Experiment 2, we assessed the semantic association between logos and food/beverage names by using a semantic priming task to elucidate whether the memory color effect of logos relates to consumer brand cognition, and found that the semantic associations between logos and food/beverage names in the high-familiarity brands were stronger than those in the low-familiarity brands only when the logos were colored correctly, but not when they were appropriately or inappropriately colored, or achromatic.

Conclusion

The current results provide behavioral evidence of the relationship between the familiarity of objects and the memory color effect and suggest that the memory color effect increases with the familiarity of objects, albeit not constantly.     

A Preconscious Neural Mechanism of Hypnotically Altered Colors: A Double Case Study

Hypnotic suggestions may change the perceived color of objects. Given that chromatic stimulus information is processed rapidly and automatically by the visual system, how can hypnotic suggestions affect perceived colors in a seemingly immediate fashion? We studied the mechanisms of such color alterations by measuring electroencephalography in two highly suggestible participants as they perceived briefly presented visual shapes under posthypnotic color alternation suggestions such as “all the squares are blue”. One participant consistently reported seeing the suggested colors. Her reports correlated with enhanced evoked upper beta-band activity (22 Hz) 70–120 ms after stimulus in response to the shapes mentioned in the suggestion. This effect was not observed in a control condition where the participants merely tried to simulate the effects of the suggestion on behavior. The second participant neither reported color alterations nor showed the evoked beta activity, although her subjective experience and event-related potentials were changed by the suggestions. The results indicate a preconscious mechanism that first compares early visual input with a memory representation of the suggestion and consequently triggers the color alteration process in response to the objects specified by the suggestion. Conscious color experience is not purely the result of bottom-up processing but it can be modulated, at least in some individuals, by top-down factors such as hypnotic suggestions.     

Vector representation of associative learning

I. P. Pavlov [12] has shown that conditioned reflexes are selective both with respect to conditioned stimuli and to conditioned reflexes elicited by those conditioned stimuli. At the neuronal level selective aspects of conditioned stimuli are based on detectors selectively tuned to respective stimuli. The selective aspects of conditioned reflexes are due to command neurons representing specific unconditioned reflexes. It can be assumed that conditioned reflexes result from association between selective detectors and specific command neurons. The detectors activated by a conditioned stimulus constitute a combination of excitations--a detector excitation vector. The detector excitation vector acts on a command neuron via a set of plastic synapses--a synaptic weight vector. Plastic synapses are modified in the process of learning making command neuron selectively tuned to a specific conditioned stimulus. The selective tuning of a particular command neuron to a specific excitation vector referred to a conditioned stimulus is a basis of associative learning. The probabilities of conditioned reflexes elicited by conditioned and differential stimuli implicitly contain information concerning excitation vectors that encode respective stimuli. Contribution of the vector code to associative learning was explored combining differential color conditioning with intracellular recording from color-coding neurons. It was shown that colors in carps and monkeys are represented on a hypersphere in the four-dimensional space similar to human color space. The basis of the color space is constituted by red-green, blue-yellow, brightness and darkness neurons.     

The connection of visual evoked potentials with the subjective differences between emotional expressions of the "schematic face"

Human cortical visual potentials (VEP) were studied to obtain electrophysiological data concerning face discrimination and to compare them with the direct estimates of differences between faces obtained in the previous publications. The present schematic faces varied in curvature of a mouth and/or declination of eyebrows. These features determined the emotional expression of the schematic faces. We recorded the VEP as the response to the instant replacement of one schematic face (referent stimulus) by an other one (test stimulus) rather then to presentation of a single stimulus. Thus we recorded direct electrophysiological differences between schematic faces. A characteristic feature of this approach was the application of the set of functionally connected test stimuli with monotonously increasing values of differences between the referent and test stimuli. In a result of analysis the complex of components P120-N180-P230 in sites O1, O2, P3, P4, T5, T6 was described. Interpeaks amplitudes of the components shows high correlations with subjective differences between the same pairs of stimuli as well as with physical (configurative) differences between stimuli measured as the angles of lines, defining curvature of a mouth and a declination of eyebrows. The highest correlation with subjective estimates of emotional differences between faces was shown by interpeaks amplitudes N180-P230 in sites O1 and P3. In the some time the interpeaks amplitudes P120-N180 in sites O1 and T5 reflected highest correlation between configurative measures and subjective estimates of stimuli differences.     

Cerebral chemosensory evoked potentials elicited by chemical stimulation of the human olfactory and respiratory nasal mucosa

A stimulation method was employed by which chemosensory evoked potentials were recorded without tactile somatosensory contamination. The purpose of the study was to determine whether potential components evoked by stimulation of the chemoreceptors of the trigeminal nerve can be distinguished from those of the olfactory nerve. The stimulants (vanillin, phenylethyl alcohol, limonene, menthol, anethol, benzaldehyde, carbon dioxide and a mixture of vanilin and carbon dioxide) were presented in a randomized order to 13 volunteers. Chemosensory evoked potentials to substances which anosmics are unable to perceive (vanillin, phenylethyl alcohol) were termed olfactory evoked potentials; potentials to CO₂, which effected no olfactory sensations were termed chemo-somatosensory potentials. Analysis of variance revealed that the different substances resulted in statistically significant changes in the amplitudes and latencies of the evoked potentials, and also in the subjective estimates of intensity. An increased excitation of the somatosensory system resulted in reduced latencies and enhanced amplitudes of the evoked potentials. Responses to the mixture of carbon dioxide and vanillin appeared significantly earlier (50–150 msec) than responses to either substance alone.     

Electric responses of the cerebral cortex to central excitation and inhibition

An attempt was made to evaluate critically the extent to which the background electrocorticogram, neuronal impulse activity, and evoked potentials reflect the state of cortical excitation and inhibition. It was shown that during electrocorticogram desynchronization, firing neurons predominated in the surface (mainly afferent) layers, while inhibited neurons were in the majority in the lower layers of the cortex. Consequently, desynchronization does not reflect diffuse excitation of the cortex and cannot be taken as an index of central excitation. Slow electrocortical waves cannot be used as indicators of an inhibitory state, even though they may be associated with processes leading to the development of inhibition. Under the effects of different stimuli, the number of neurons participating in impulse condition, and the number of neurons temporarily inhibiting impulse activity in the projection cortical area were stable (ratio 2:1). It was found that the correlation between impulse discharges of neuronal pairs increases during both central excitation and central inhibition. Nonetheless, differences between cortical excitation and inhibition were seen in the reorganization of neuronal columns. The use of evoked potentials to determine cortical excitation or inhibition is complicated by the fact that the amplitude of evoked-potential components reflects the divergent influences of many factors. It was shown that conditional excitation diminished the evoked potential to a light stimulus in the projection cortical area, but caused it to increase in the region of the motor analyzer. The elaboration of a conditional inhibition (extinction) is accompanied by the growth of an evoked potential to a stimulus in the primary cortical area, and by its repression in the region of the motor analyzer. In this case, a large delayed negative wave appears in the evoked potential.This report was presented at the All-Union Symposium on Electric Responses of the Cerebral Cortex to Afferent Stimuli, Kiev, October, 1969.Rostov-on-Don State University. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 140–154, March–April, 1970.     

Perception matches selectivity in the human anterior color center

Human ventral cortex contains at least two visual areas selective for color [1]: a posterior center in the lingual gyrus labeled V4 [2-4], V8 [5], or VO-1 [6] and an anterior center in the medial fusiform that has been labeled V4alpha[3, 4]. We examined the properties of the anterior color center using electrical recording and electrical stimulation in a subject with an electrode implanted over the anterior color center, as determined with BOLD fMRI in the same subject. Presentation of visual stimuli evoked local field potentials from the electrode. Consistent with fMRI, the potentials were larger for chromatic than achromatic stimuli. The potentials differed depending on stimulus color, with blue-purple colors evoking the largest response. The spatial receptive field of the electrode was central/parafoveal with a contralateral bias. In the absence of a visual stimulus, electrical stimulation of the electrode produced an artificial visual percept of a blue-purple color near the center of gaze. These results provide direct evidence of a tight link between selectivity and perception in ventral temporal cortex. Electrical stimulation of the anterior color center is sufficient to produce the conscious percept of a color whose identity is determined by the selectivity of the stimulated neurons.     

Influence of segmental and extra-segmental conditioning stimuli on cortical potentials evoked by painful electrical stimulation

This study evaluated the effects of two different types of segmental/extra-segmental conditioning stimuli (tonic muscle pain and non-painful vibration) on the subjective experience (perceived pain intensity) and on the cortical evoked potentials to standardized test stimuli (cutaneous electrical stimuli). Twelve subjects participated in two separate sessions to investigate the effects of tonic muscle pain or cutaneous vibration on experimental test stimuli. The experimental protocol contained a baseline registration (test stimuli only), a registration with the test stimuli in combination with the conditioning stimuli, followed by a registration with the test stimuli only. In addition, the effects of the conditioning stimuli were examined at two anatomically separated locations (segmental and extra-segmental). Compared with the test stimulus alone, the perceived pain intensity and peak-to-peak amplitudes of the evoked potentials were unchanged in the presence of non-painful conditioning stimuli at either location. In contrast, a significant decrease of the perceived pain intensity and peak-to-peak amplitudes was found in the presence of painful conditioning stimuli at the extra-segmental sites. Moreover, the topographic maps of the 32-channel recordings suggested that the distribution of the scalp evoked potentials was almost symmetrical around the vertex Cz in the baseline registration. The evoked potentials were generally decreased during hypertonic saline infusion at the extra-segmental sites, but the distribution of the topographic maps did not appear to change. Vibration has previously been shown to inhibit pain, but in the present study the perceived intensity of phasic painful electrical stimuli was unchanged. The reduced perceived pain intensity and the smaller peak-to-peak amplitude of the evoked potential in the presence of extra-segmental conditioning pain are in accordance with the concept of diffuse noxious inhibitory control.     

Fechner-Benham subjective colors do not induce McCollough after-effects

Fechner-Benham subjective color is widely believed to be governed by local interactions in early (probably retinal) mechanisms. Here we report three lines of phenomenological evidence that suggest otherwise: subjective colors seen in spatially extended stimuli (a) are dependent on global aspects of the stimuli; (b) can become multistable in position; and (c) even after being stabilized do not support the creation of McCollough's colored after-effects--a cortically based phenomenon generally thought to be more central than Fechner-Benham color. These phenomena suggest a central locus that controls perception of subjective color, characterized by pattern dependent interactions among cortical mechanisms that draw their inputs from peripheral units.     

Excitation of cat spinal cord dorsal column fibers during stimulation of different fiber groups of cutaneous and somatic nerves

The effects of electrically stimulating different groups of nerve fibers supplying the skin and muscle on evoked potentials in cat spinal cord dorsal columns were studied. Significant differences in the configuration of dorsal column potentials recorded in response to stimulation of these nerves were found. It was shown that cutaneous nerve unmyelinated fibres were connected to unmyelinated dorsal column fibers. In addition, excitation of cutaneous C-fibers lead to activation of dorsal column fibers with the maximum conduction velocity. The somatic nerve was only connected to myelinated dorsal column fibers, and excitation of its non-myelinated fibers did not cause other types of dorsal column fibers to be activated. It is suggested that the acceleration of cutaneous signal transmission in the dorsal column system may be brought about by the necessity for rapid warning of potentially harmful stimuli.Medical Institute, Russian Federation Ministry of Public Health, Nizhny Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 625–635, September–October, 1992.     

Comparison of evoked potentials to tones and clicks recorded simulataneously by multiple electrodes from the auditory cortex in unanesthetized cats

Evoked potentials to tones and clicks were recorded simultaneously from seven points of the auditory cortex and one or two points of the somatosensory cortex in unanesthetized cats. Comparison of evoked potentials to tones of equal loudness in the 250–7000 Hz band showed no common pattern of cortical tonotopic distribution. However, an individual dependence of the components of the evoked potential on pitch and on localization of the recording point exists for each animal. With a change in stimulus intensity the absolute and relative values of these components of the evoked potential vary. The initial positive waves are the most variable; besides the two waves already known a third, intermediate wave, particulary sensitive to loudness, was discovered. The negative wave of the primary response increases proportionally to loudness. Evoked potentials to clicks are more uniform over the auditory cortex and more stable than those to tones. Responses appeared in the somatosensory cortex to loud stimuli, more regularly to clicks than to tones. It is concluded that the parameter of pitch is reflected in the cat cortex as a complex spatially-individual distribution of the amplitude and time parameters of the evoked potentials.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 7, No. 2, pp. 115–125, March–April, 1975.     

Computation of responses to color and brightness differences of neurons in the rabbit lateral geniculate nucleus

Changes in activity of 51 neurons in the rabbit lateral geniculate nucleus evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. It was found that neurons displayed the earliest phasic (within 50-90 ms after the replacement) and tonic response components. The earliest component strongly correlated with differences between stimuli, whereas the tonic component depended on stimuli intensity. Analysis of phasic component revealed two neuronal populations: the first group of cells was specialized for stimuli differentiation only by their intensities, and, and the second group could measure differences in colors and intensities. Neuronal perceptual spaces were reconstructed using the average of the earliest response component as a measure of differences between stimuli. Spaces of 44 neurons (86%) were two-dimensional with brightness and darkness axes. Such neurons had the same structures of space for color and achromatic stimuli. Spaces of 7 neurons (14%) were four-dimensional with two chromatic and two achromatic axes. The structures of perceptual space reconstructed from neurons in the lateral geniculate nucleus were identical to the spaces calculated from the neurons in the primary visual cortex. The structure of the perceptual space reconstructed from neuronal spikes was also similar to space calculated from the N85 visual evoked potential component recorded under similar conditions and to another space reconstructed on the basis of rabbit's instrumental learning. This fact confirmed the general principle of vector coding in the visual system. The tonic component of the most of neurons in the lateral geniculate nucleus showed a linear correlation with changes in intensities, thereby these neurons could be characterized as pre-detectors for cortical selective detectors.     

A geometrical model for the perceived line of orientation based on subjective evaluations and human VEP data

A geometric model in proposed based on subjective dissimilarity estimates among differently oriented line segments in the frontal plane and on visual evoked potentials (VEP) recorded in respond to abrupt changes in the orientation of such a line segment. The orientations are represented by points constituting a clised planar curve, with interpoint distances corresponding to interstimulus dissimilarities. The angle of the radius-vertor connecting the center of the configuration with its circumference encodes the orientation of the line stimuli in the visual field, and two Cartesian axes drawn through the center are interpreted as two orientation-opponent channels in the neuronal network processing line orientation. The first channel (the ordinate axis) gives maximal positive and maximal negative responses to, respectively, vertical and horizontal orientations, whereas the second channel (the abscissa axis) gives maximal positive and maximal negative responses to, respectively, 45 and 135 degrees orientations. The VEP analysis shows that the activity of the first channel affects the interpeak amplitudes of both the P1-N2 (P130-N180) and N2-P2 (N180-P230) components, whereas the second channel affects only the late component N180-P230. We propose the hypothesis according to which outputs of the two channels are connected linearly (which is reflected in the city-block metric obtained when distances are computed directly from neuronal activity), but the growth rate of the overall output is inhibited nonlinearly when it reaches large absolute values. This inhibition effectively transforms the "true" city-block metric of the line orientation space into the Euclidean metric one obtains when distances are computed from subjective dissimilarity estimates. VEP amplitudes as intermediate characteristics of visual processing between neuronal activity and subjective estimates represent intermediate metric (between city-block and Euclidean).     

Relation of visual evoked potentials to the integral characteristics of cognitive activity in 8- to 9-year-old children

Amplitude and temporal parameters of evoked potentials (EPs) in response to a checkerboard pattern, picture of a house, the Russian word "dom", meaning house, combination of letters "DMO" and a number of other stimuli, correlated with indices of the verbal, nonverbal, and general intelligence as well as with those of the cognitive style "field dependence-independence". Maximum number of statistically significant correlations was found in the course of comparison of integrative cognitive characteristics and parameters of EPs to stimuli with increased semantic complexity. No interhemispheric differences were found in the character of interrelations between cognitive characteristics and parameters of EPs to verbal and spatially structured stimuli.     

Unconscious letter discrimination is enhanced by association with conscious color perception in visual form agnosia

Adaptive behavior guided by unconscious visual cues occurs in patients with various kinds of brain damage as well as in normal observers, all of whom can process visual information of which they are fully unaware [1] [2] [3] [4] [5] [6] [7] [8]. Little is known on the possibility that unconscious vision is influenced by visual cues that have access to consciousness [9]. Here we report a 'blind' letter discrimination induced through a semantic interaction with conscious color processing in a patient who is agnosic for visual shapes, but has normal color vision and visual imagery. In seeing the initial letters of color names printed in different colors, it is normally easier to name the print color when it is congruent with the initial letter of the color name than when it is not [10]. The patient could discriminate the initial letters of the words 'red' and 'green' printed in the corresponding colors significantly above chance but without any conscious accompaniment, whereas he performed at chance with the reverse color-letter mapping as well as in standard tests of letter reading. We suggest that the consciously perceived colors activated a representation of the corresponding word names and their component letters, which in turn brought out a partially successful, unconscious processing of visual inputs corresponding to the activated letter representations.     

Topographic analysis of auditory event-related potentials associated with acoustic and semantic processing

The topography of auditory event-related potentials (ERPs) was examined during 3 kinds of tasks: selection of a specified real word or nonsense syllable from a list; simple detection of each of the same stimuli without discrimination; and classification of a set of words according to a specified semantic category. The potentials that were associated with the additional processing required by the discriminative tasks were disclosed by subtracting the wave forms obtained in the detection condition from those obtained during discriminative performance. Difference wave forms were also derived between the semantic classification and verbal discriminative ERP to delineate the changes associated with the extraction of word meaning.The topography of the ERP associated with stimulus detection was comparable to that found in previous studies of evoked potentials to non-speech stimuli. This distribution was consistent with 2 cortical generators, one within the supratemporal plane and the other on the lateral surface of the superior temporal gyrus. When discriminative performance was required on the basis of acoustic stimulus properties, the topography of the difference wave form that reflected this discriminative processing extended more posteriorly over temporal cortex. Semantic processing elicited a further posterior extension of ERP components by 330 msec after stimulus onset, as well as longer latency potentials that were not present in the verbal selection task. These differences imply that a more extensive portion of language cortex is engaged in semantic classification than in verbal identification.     

Operative memory and evoked visual potentials

Changes in human EEG and event-related potentials to the complex color stimulus were studied during performance of three cognitive tasks: passive viewing, visual searching, and memorizing and storing of the stimulus in the operative memory. It was shown that involvement of memory mechanisms resulted in the alpha rhythm suppression in both occipital and frontal brain areas. It was also accompanied by a generation of the slow positive component in the evoked potential recorded in the frontal areas (in the occipital areas this wave was manifested as negative).     

A LABELED AFFECTIVE MAGNITUDE (LAM) SCALE FOR ASSESSING FOOD LIKING/DISLIKING1

The most widely used scale for assessing food liking or disliking is the 9‐pt hedonic scale. Unfortunately, this affective scale suffers from problems related to unequal scale intervals and the underuse of end categories, which results in a reduced ability to differentiate among extremely well liked or extremely disliked foods. Magnitude estimation avoids these problems while enabling ratio statements to be made about the data. However, it does not provide absolute ratings of liking/disliking and can be difficult for some consumers to use. We report here on the development of a labeled affective magnitude scale (LAM) scale that has advantages over both the 9‐pt hedonic scale and magnitude estimation. Forty‐four semantic labels were scaled for their affective meaning by subjects using modulus‐free magnitude estimation. The geometric mean magnitude estimates obtained for each semantic label were used to construct a series of labeled affective magnitude scales by spacing the labels along a visual analogue scale according to their obtained semantic values. Reliability and sensitivity studies were conducted to assess the effects of alternative semantic and numeric labels. The results of these studies led to the choice of a scale format that uses verbal labels that are consistent with the 9‐pt hedonic scale. The labeled affective magnitude (LAM) scale was compared to the hedonic scale and magnitude estimation in several food preference and acceptability tests. The LAM was shown to have equal reliability and sensitivity to the hedonic scale, provided somewhat greater discrimination among highly liked foods, and resulted in data that were similar to magnitude estimation in terms of the obtained ratios among rated stimuli. The LAM scale was also judged by consumers to be as easy to use as the 9‐pt hedonic scale and significantly less difficult than magnitude estimation.     

Electrophysiological Correlation of the Degree of Self-Reference Effect

The present study investigated neural correlations underlying the psychological processing of stimuli with various degrees of self-relevance. Event-related potentials were recorded for names that differ in their extent of relevance to the study participant. Participants performed a three-stimulus oddball task. ERP results showed larger P2 averaged amplitudes for highly self-relevant names than for moderately self-relevant, minimally self-relevant, and non-self-relevant names. N2 averaged amplitudes were larger for the highly self-relevant names than for the moderately self-relevant, minimally self-relevant, and non-self-relevant names. Highly self-relevant names elicited larger P3 averaged amplitudes than the moderately self-relevant names which, in turn, had larger P3 values than for minimally self-relevant names. Minimally self-relevant stimuli elicited larger P3 averaged amplitudes than non-self-relevant stimuli. These results demonstrate a degree effect of self-reference, which was indexed using electrophysiological activity.