Differences in color fading and recovery under sustained fixation

More than two centuries ago, Swiss philosopher I. P. V. Troxler announced in 1804 that fixated images fade away during normal vision. Since this declaration, the phenomenon now known as Troxler fading has become the subject of intensive research. Many researchers were eager to find out why we experience image fading and under what conditions image restoration happens. Here, we investigated the dynamics of color stimulus fading and recovery under sustained eye fixation. The objective of the experiments was to find out which colors fade and recover faster under isoluminant conditions. The stimuli were eight blurred color rings extending to 13° in size. Four unique colors (red, yellow, green, and blue) and four intermediate colors (magenta, cyan, yellow-green, and orange) were used. Stimuli were displayed on a computer monitor with a gray background and were isoluminant to the background. The presentation of the stimulus lasted 2 min and subjects were required to look at the fixation point in the middle of the ring and suppress eye movements. The task for subjects was to report the moments of change in the stimulus visibility by four stages of stimulus completeness. We found that all investigated colors undergo fading and recovery cycles during 2 min of observation. The data suggest that magenta and cyan colors have faster stimulus fading and undergo more recovery cycles, while longer wavelength colors slow down stimulus fading.

Facial Muscles Reactions to Other Person’s Facial Expressions of Pain

The aim of this study was to record facial electromiograms (EMG) while subjects were viewing facial expressions of different pain levels (no-pain, medium pain and very painful) and to find objective criteria for measuring pain expressed in human’s face. The study involved 18 students with age 21 years. The magnitude of the EMG response of m. corrugator supercilii depended on voluntary performed facial pain expression in the subjects. EMG responses of voluntary performed facial pain expressions to mirrored pain reactions were detected at two time span intervals: 200–300 ms after stimulation in m. zygomaticus major, and 400–500 ms after stimulation in m. corrugator supercilii. These differences disappear after 1300 ms. In the second time interval, differences in EMG responses of both muscle groups occur 1600 ms after stimulus presentation, but disappear differently: 3100 ms after stimulation in m. zygomaticus major and 4000 ms in m. corrugator supercilii. Constant responding with “medium pain” expression when recognizing faces of different pain expressions have an effect on the voluntary EMG responses of individual subjects. Images with emotional expression “no pain” reduce m. corrugator supercilii activity and increase m. zygomaticus major activity for those observers.

Neural Model of Coding Stimulus Orientation and Adaptation

The coding of line orientation in the visual system has been investigated extensively. During the prolonged viewing of a stimulus, the perceived orientation continuously changes (normalization effect). Also, the orientation of the adapting stimulus and the background stimuli influence the perceived orientation of the subsequently displayed stimulus: tilt after-effect (TAE) or tilt illusion (TI). The neural mechanisms of these effects are not fully understood. The proposed model includes many local analyzers, each consisting of two sets of neurons. The first set has two independent cardinal detectors (CDs), whose responses depend on stimulus orientation. The second set has many orientation detectors (OD) tuned to different orientations of the stimulus. The ODs sum up the responses of the two CDs with respective weightings and output a preferred orientation depending on the ratio of CD responses. It is suggested that during prolonged viewing, the responses of the CDs decrease: the greater the excitation of the detector, the more rapid the decrease in its response. Thereby, the ratio of CD responses changes during the adaptation, causing the normalization effect and the TAE. The CDs of the different local analyzers laterally inhibit each other and cause the TI. We show that the properties of this model are consistent with both psychophysical and neurophysiological findings related to the properties of orientation perception, and we investigate how these mechanisms can affect the orientation's sensitivity.

Fast cyclic stimulus flashing modulates perception of bi-stable figure

Many experiments have demonstrated that the rhythms in the brain influence the initial perceptual information processing. We investigated whether the alternation rate of the perception of a Necker cube depends on the frequency and duration of a flashing Necker cube. We hypothesize that synchronization between the external rhythm of a flashing stimulus and the internal rhythm of neuronal processing should change the alternation rate of a Necker cube. Knowing how a flickering stimulus with a given frequency and duration affects the alternation rate of bistable perception, we could estimate the frequency of the internal neuronal processing. Our results show that the perception time of the dominant stimulus depends on the frequency or duration of the flashing stimuli. The duration of the stimuli, at which the duration of the perceived image was maximal, was repeated periodically at 4 ms intervals. We suppose that such results could be explained by the existence of an internal rhythm of 125 cycles/s for bistable visual perception. We can also suppose that it is not the stimulus duration but the precise timing of the moments of switching on of external stimuli to match the internal stimuli which explains our experimental results. Similarity between the effects of flashing frequency on alternation rate of stimuli perception in present and previously performed experiment on binocular rivalry support the existence of a common mechanism for binocular rivalry and monocular perception of ambiguous figures.

Influences of prolonged viewing of tilted lines on perceived line orientation: the normalization and tilt after-effect

Gibson [J. Exp. Psychol. 16, 1 (1993)] observed that during prolonged viewing, a line perceptually rotates toward the nearest vertical or horizontal meridian (the normalization effect), and moreover, the perceived orientation of a subsequently presented line depends on the orientation of the adapting one (the tilt after-effect). The mechanisms of both phenomena remain poorly understood. According to our experimental results, the adapting line perceptually rotates to the nearest of three orientations: vertical, horizontal, and diagonal. We propose a simple neuronal model of orientation detectors whose responses are determined by the cardinal detectors. It is shown that both normalization and tilt after-effect may be explained by adaptation of these cardinal detectors.

A comparison of the Hand Test results of Finnish and Lithuanian school children

Although the Hand Test (HT) scores should be cautiously approached when using individuals from different cultures, the quantitative results of Finnish and Lithuanian groups of 13 year old children seem to be in line with Stetson's and Wagner's (1980) hypothesis on potential use of HT in different cross­cultural studies. Finnish children scored higher on Exhibition, Active, Tension, Fear subcategories, on Environmental and Maladjustive combined categories, also on Total Number of Responses and Average initial Response Time. Lithuanian children scored higher on Description subcategory. The differences were more marked between the Finnish and Lithuanian girls than between the boys of these nations. The results are fixed as a starting point for /ong-term cross-cultural research.

The originalities of ethnically determined psychic phenomena of Aukštaičiai and Žemaičiai individuals

The purpose of the research work was to compare psychic characteristics of elderly (60-85 years old) Aukštaičiai (people of the Lithuanian highlands) and Žemaičiai (people of the Lithuanian lowlands). The most important point was to distinguish ethnically determined differences in the research object. The nuli hypothesis on the absence of distinguishing psychic characteristics between the sample of 60 elderly Aukštaičiai individuals and the sample of 60 Žemaičiai individuals was verified by means of empirical research. The Rorschach Inkblot Method and the full Lūscher Color Test were used in the research work. Of 30 examined by Rorschach lnkblot Method variables, 13 showed a statistically significant difference. A representation of 13 variables of the method did not support the nuli hypothesis on the homogeneity of Aukštaičiai and Žemaičiai samples. The variables W, D, Dd, M, H, A, Ad, 11, Z, Egol, IsI, R, and t statistically show significant differences in results of the Aukštaičiai and Žemaičiai investigation. Full Lūscher Color Test results differentiated the groups according to the choice of red color in the basic 8-colour table. According to the results, 3 basic groups of ethnically determined psychic phenomena and their peculiarities were identified, i.e., cognitive processes, emotional experiences, and personality traits. lndividuals belonging to the samples also differed in the character of their relations with the material and social environment. Ethnically determined psychic phenomena and their peculiarities could have formed owing to the influence exercised by variables that fall into 6 groups: the physical environment, social structure, subjective culture, personality, personality predispositions, and accidental factors. The results of the research were fixed as a starting point for exhaustive and long-term ethnopsychological investigations and as tasks to be concluded in further ethnopsychological research in Lithuanian programs.