Power spectral density changes in the EEG during mental arithmetic and eye-opening

Summary The effect of mental arithmetic (standard multiplication, with eyes closed) and eye-opening on the power spectral density of the EEG (recorded bipolarly from occipital and parietal regions) have been compared. The EEG was recorded on magnetic tape from normal subjects, (medical students) in a constant environment and subsequently analysed by an analogue computer (Noratom Instrument for Statistical Analysis and Computation, ISAC).Absolute measurements made from 15 subjects with eyes closed have shown that peaks of power at 10 Hz vary from 9 to 46 V² per Hz. Qualitatively, suppression of power at 10 Hz is greater due to eye-opening than mental arithmetic.Analysis of pooled power spectral density functions from 11 subjects showed that the effect of eye-opening differed significantly from the effect of mental arithmetic at 2.5 and 12.5 Hz. Suppression of lower frequency alpha activity was more pronounced during calculation than during eye-opening. Compared with the eyes closed condition, eye-opening showed a highly significant suppression at 10 and 12.5 Hz (alpha activity) and from 15 to 25 Hz (beta activity). Mental arithmetic induced significant suppression at 7.5 and 10 Hz and from 15 to 30 Hz. Eye-opening enhanced lower frequency activity which calculation suppressed.Variation was greater between first, second and third calculations in pooled power spectral densities than between corresponding eye-opening epochs. It is suggested that these differences in effects of eye-opening and mental arithmetic reflect differences in underlying cerebral activity, rather than that an underlying factor common to both effects may be orbital in origin.     

Theta activity and meditative states: spectral changes during concentrative meditation

Brain oscillatory activity is associated with different cognitive processes and plays a critical role in meditation. In this study, we investigated the temporal dynamics of oscillatory changes during Sahaj Samadhi meditation (a concentrative form of meditation that is part of Sudarshan Kriya yoga). EEG was recorded during Sudarshan Kriya yoga meditation for meditators and relaxation for controls. Spectral and coherence analysis was performed for the whole duration as well as specific blocks extracted from the initial, middle, and end portions of Sahaj Samadhi meditation or relaxation. The generation of distinct meditative states of consciousness was marked by distinct changes in spectral powers especially enhanced theta band activity during deep meditation in the frontal areas. Meditators also exhibited increased theta coherence compared to controls. The emergence of the slow frequency waves in the attention-related frontal regions provides strong support to the existing claims of frontal theta in producing meditative states along with trait effects in attentional processing. Interestingly, increased frontal theta activity was accompanied reduced activity (deactivation) in parietal–occipital areas signifying reduction in processing associated with self, space and, time.     

Perception in chess

This paper develops a technique for isolating and studying the perceptual structures that chess players perceive. Three chess players of varying strength — from master to novice — were confronted with two tasks: (1) A perception task, where the player reproduces a chess position in plain view, and (2) de Groot's (1965) short-term recall task, where the player reproduces a chess position after viewing it for 5 sec. The successive glances at the position in the perceptual task and long pauses in the memory task were used to segment the structures in the reconstruction protocol. The size and nature of these structures were then analyzed as a function of chess skill.     

Perception of the length of an object through dynamic touch is invariant across changes in the medium

Rotational inertia—a mechanical quantity that describes the differential resistance of an object to angular acceleration in different directions—has been shown to support perception of the properties of that object through dynamic touch (wielding). The goal of the present study was to examine if perception of the length of an object through dynamic touch depends on its rotational inertia, independent of the medium in which it is wielded. The participants (n = 14) wielded 12 different objects held in air or completely immersed in water and reported perceived lengths of those objects. Each object consisted of a rod of a particular density with a particular number of stacked steel rings attached at a particular location along its length. Perceived length was invariant across medium. In addition, a single-valued function of the major eigenvalue, I ₁, and the minor eigenvalue, I ₃, of the rotational inertia, I, of the 12 objects predicted the perceived lengths of those objects in both air and water, and the perceived lengths were invariant across the two media. These results support the hypothesis that the informational support for perception of the length of an object through dynamic touch is invariant across changes in the medium.     

Perception of clicks in music

Subjects were asked to judge the position of a click that occurred during a short piece of music. Clicks were, on average, judged to be later than their actual position. The click and the music were presented through headphones to different ears, and the clicks were judged to be significantly later if they arrived at the right ear rather than at the left. There was also a significant tendency for clicks to be attracted to phrase boundaries in the music. These last two results are similar to those from experiments with a click during speech, but the late judgments of a click in music contrast with the early judgments of a click in speech.     

Perception of resyllabification in French

In three experiments, we examined the effects of phonological resyllabification processes on the perception of French speech. Enchainment involves the resyllabification of a word-final consonant across a syllable boundary (e.g., in chaque avion, the /k/ crosses the syllable boundary to become syllable initial). Liaison involves a further process of realization of a latent consonant, alongside resyllabification (e.g., the /t/ in petit avion). If the syllable is a dominant unit of perception in French (Mehler, Dommergues, Frauenfelder, & Segui, 1981), these processes should cause problems for recognition of the following word. A cross-modal priming experiment showed no cost attached to either type of resyllabification in terms of reduced activation of the following word. Furthermore, word- and sequence-monitoring experiments again showed no cost and suggested that the recognition of vowel-initial words may be facilitated when they are preceded by a word that had undergone resyllabification through enchainment or liaison. We examine the sources of information that could underpin facilitation and propose a refinement of the syllable's role in the perception of French speech.     

Perception of gait

Our ability of perceive the identity and naturalness of a human gait is examined in a series of four experiments involving computer-animated stick figures. The results indicate that the perceived naturalness of a walking or running gait can be influenced by the motion of any limb segment, but the perceived identity of these gaits is primarily determined by the movements of the lower leg (i.e., the tibia). The results also demonstrate that a perceptually salient walking gait can be transformed into running (or vice versa) by adding or subtracting a constant value to the angle of the lower leg over the entire step cycle. The size of this constant value is affected by the shape of the lower leg angle function and the motion of other limb segments.     

Perception of illumination

Abstract.— Previous research on the perception of illumination has primarily been occupied with the apparent paradox that "we must know the object colour in order to utilize the reflected light as an index of illumination, while we must know the illumination in order to use the reflected light as an index of object colour". The present study shows this paradox to exist only as a long as the traditional one-dimensional conception of achromatic colours is maintained. Two experiments are reported. In Exp. 1 it is shown that by mere variation of the luminance difference of two adjacent areas, a consistent shift in colourlshadow discrimination is obtained; i.e. within a certain range of luminance differences the observer may find it difficult to decide whether the difference is one of colour (two fields of different greyness in common illumination) or one of illumination (two fields of equal greyness under different illumination), above this range the observer perceives the differences as one of illumination. Taking the bidimensionality of achromatic colours into account in Exp. 2, results are obtained which show the brightness (alternatively termed luminosity) relations of adjacent areas to be the critical factor for the perceptual shift.     

Perception of sequence in auditory events

A series of tape-recorded sentences were presented to various groups of listeners, totalling 164. During each sentence an extraneous sound was present on the recording, and the listener had to indicate the exact point in the sentence at which this sound occurred. It was found that errors were made which were large compared with the duration of a single speech sound; which suggests that the listener does not deal with each sound separately but rather with a group of sounds. Errors were reduced if the sentence consisted of a series of digits rather than an ordinary text, or if the listeners were trained in phonetics. Prior knowledge of the content of the sentence did not affect accuracy. The direction of error was usually to refer the extra sound to an early point, but it is affected by the relative position of the extra sound in the sentence. These results can be regarded as an extension, to the case where all stimuli are presented to the same sense, of classic results on prior entry.     

Perception of clusters in statistical maps

Two experiments observed performance on a cluster identification task across a variety of common statistical maps. Stimulus maps displayed mortality rates for several diseases and subjects had to identify regions of the map that were perceived to form a cluster of particularly high (or low) mortality. Subjects marked the perceived centroid of each cluster, and analyses focused on the dispersion of centroid location across subjects. Under these circumstances, monochrome classed choropleth maps were found to minimize dispersion, compared to a two opposing colours scheme, a dot density map, a pie map, and a categorical (hue-based) colour scheme. Maps using a familiar geographical unit (i. e. a U. S. state) supported better recall of the information than maps using less familiar and smaller geographical units. The results were found to be interpretable within current cognitive theory.     

Perception in consequences of free riding

This study examined the relationships between perceptions of group members' free riding and group outcomes using Mulvey and Klein's 1998 perceived free riding scale. In a laboratory study, three free riding conditions were created (no free riding, free riding, free riding with justification) in which 97 college students performed two short number-finding tasks as members of temporary ad hoc three-person groups. 55% of the students were male and the average age was 22.9 yr. (SD= 3.0). Participants' perceptions of free riding were negatively related to commitment to the assigned group goal, task performance, and goals for group performance and individual performance. In the condition wherein free riding was justified by low ability, participants set lower goals for their future task performance than did those in the other two conditions.     

Perception of risk in genetic counseling

Abstract

Genetic counseling is a psychological process of communicating and perceiving information about risks. As such, it is important to assess how information is understood by counselees and how psychological factors affect risk perception. Subjects were 76 patients at a genetic clinic whose understanding of genetic counseling was assessed, along with their motivation and way of thinking about risks. Results indicated that subjective interpretations of recurrence risks are better predictors of their reproductive intentions than the “objective” risks. Also, specific cognitive and motivational factors appear to explain much of the variance in risk perception in genetic counseling. The results have important implications for how counseling is conducted, as well as for theoretical issues about cognitive processes.     

Perception of structure in novel music

Two experiments demonstrated the way in which musicians and nonmusicians process realistic music encountered for the first time. A set of tunes whose members were related to each other by a number of specific musical relationships was constructed. In Experiment 1, subjects gave similarity judgments of all pairs of tunes, which were analyzed by the ADDTREE clustering program. Musicians and nonmusicians gave essentially equivalent results: Tunes with different rhythms were rated as being very dissimilar, whereas tunes identical except for being in a major versus a minor mode were rated as being highly similar. In Experiment 2, subjects learned to identify the tunes, and their errors formed a confusion matrix. The matrix was submitted to a clustering analysis. Results from the two experiments corresponded better for the nonmusicians than for the musicians. Musicians presumably exceed nonmusicians in the ability to categorize music in multiple ways, but even nonmusicians extract considerable information from newly heard music.     

Perception of serial order in infants

Serial order is fundamental to perception, cognition and behavioral action. Three experiments investigated infants' perception, learning and discrimination of serial order. Four- and 8-month-old infants were habituated to three sequentially moving objects making visible and audible impacts and then were tested on separate test trials for their ability to detect auditory, visual or auditory-visual changes in their ordering. The 4-month-old infants did not respond to any order changes and instead appeared to attend to the 'local' audio-visual synchrony part of the event. When this local part of the event was blocked from view, the 4-month-olds did perceive the serial order feature of the event but only when it was specified multimodally. In contrast, the 8-month-old infants perceived all three kinds of order changes regardless of whether the synchrony part of the event was visible or not. The findings show that perception of spatiotemporal serial order emerges early in infancy and that its perception is initially facilitated by multimodal specification.     

Perception of motion in equiluminous kinematograms

Two fields of random dots that were identical except for a slight shift in a central square region were presented in rapid alternation. This produced a vivid impression of a square moving back and forth above the background. When the kinematogram is presented in equiluminous red/green, the motion of the central region can still be seen, although over a narrower range of alternation rates, interstimulus intervals, and displacements than for black/white presentation. The perception of motion for equiluminous stimuli indicates that colour and motion can be analyzed conjointly by the visual system. However, as originally reported by Ramachandran and Gregory, the segregation of the oscillating central square from the background is lost at equiluminance. This segregation process therefore appears to be colour-blind.