Norman D. Cook

Intermanual transfer of proximal and distal motor engrams in humans

We studied intermanual motor transfer for right-to-left or left-to-right direction of transfer between either proximal or distal upper extremity muscle groups. The influence of previously acquired motor engrams (original learning, OL) on learning efficiency of the contralateral side (transfer learning, TL) was examined in 26 right-handed healthy subjects. The task consisted of the drawing of meaningless figures. During TL, OL figures had to be reproduced as vertical mirror reversals. Data revealed a benefit for right-to-left but not left-to-right direction of transfer for time to complete a figure as well as a left-to-right transfer benefit for spatial motor precision. Furthermore, a benefit for intermanual transfer of training between proximal but not distal muscle groups was found when movement time to complete a figure was evaluated. Of special interest was the observation of a disadvantage due to prior contralateral learning for performance at right distal effectors. The asymmetrical transfer benefits with respect to side are in line with previous findings and support the proficiency model and the cross-actiation model. Results further showed that intermanual transfer of training might differ with respect to muscle group involvement and suggest that, although primarily facilitating, previous opposite hand training may lead to inhibitory influences on subsequent contralateral reproduction.

The internal clock: Electroencephalographic evidence for oscillatory processes underlying time perception

It has been proposed that temporal perception and performance depend on a biological source of temporal information. A model for a temporal oscillator put forward by Treisman, Faulkner, Naish, and Brogan (1990) predicted that if intense sensory pulses (such as auditory clicks) were presented to subjects at suitable rates they would perturb the frequency at which the temporal oscillator runs and so cause over- or underestimation of time. The resulting pattern of interference between sensory pulse rates and time judgments would depend on the frequency of the temporal oscillator and so might allow that frequency to be estimated. Such interference patterns were found using auditory clicks and visual flicker (Treisman & Brogan, 1992; Treisman et al., 1990). The present study examines time estimation together with the simultaneously recorded electroencephalogram to examine whether evidence of such an interference pattern can be found in the EEG. Alternative models for the organization of a temporal system consisting of an oscillator or multiple oscillators are considered and predictions derived from them relating to the EEG. An experiment was run in which time intervals were presented for estimation, auditory clicks being given during those intervals, and the EEG was recorded concurrently. Analyses of the EEG revealed interactions between auditory click rates and certain EEG components which parallel the interference patterns previously found. The overall pattern of EEG results is interpreted as favouring a model for the organization of the temporal system in which sets of click-sensitive oscillators spaced at intervals of about 12.8 Hz contribute to the EEG spectrum. These are taken to represent a series of harmonically spaced distributions of oscillators involved in time-keeping.

Hemispheric dissociation in judging semantic relations: complementarity for close and distant associates.

In two lateralized tachistoscopic experiments, we presented (i) pairs of nouns with close or distant semantic associations or (ii) pairs of nouns which were randomly matched and later rated by the subjects as to their semantic distance. In both experiments, words presented to the right visual field were more frequently judged as semantically close in meaning than words presented to the left visual field (LVF), whereas words presented to the LVF were more frequently judged as semantically distant. The results are discussed in relation to hemispheric language functions and current models of cerebral laterality.

‘Meaningful’ Patterns in Visual Noise: Effects of Lateral Stimulation and the Observer’s Belief in ESP

Visual noise subjectively contains more meaningful patterns (1) when tachistoscopically presented to the left visual field, and (2) for persons who believe in extrasensory perception (ESP). These results indicate a possible right hemisphere mediation of delusional perception and suggest some delusional component in the belief in ESP.

The case for reverse translation.

The case for “reverse translation” is briefly presented. The manifest problems in immunology in accounting for antibody diversity and the dependence of DNA mutation on cellular processes plus, on the theoretical side, the cybernetic necessity of abstracting environmental information in order to maintain relevant genetic material together give weight to a search for this reverse process. Meklers 1967 reverse translation theory is outlined and shown not to be objectionable either in terms of known biochemical reactions or in terms of the assertion of the “central dogma” that macro-molecular information does not “flow out” of the proteins once it has “flowed in”.

Effects of visual-field inversions on the reverse-perspective illusion.

The ‘reverse-perspective’ illusion entails the apparent motion of a stationary scene painted in relief and containing misleading depth cues. We have found that, using prism goggles to induce horizontal or vertical visual-field reversals, the illusory motion is greatly reduced or eliminated in the direction for which the goggles reverse the visual field. We argue that the illusion is a consequence of the observers inability to reconcile changes in visual information due to body movement with implicit knowledge concerning anticipated changes. As such, the reverse-perspective illusion may prove to be useful in the study of the integration of linear perspective and motion parallax information.

Hemispheric Cooperation in Visuospatial Rotations: Evidence for a Manipulation Role for the Left Hemisphere and a Reference Role for the Right Hemisphere

A survey of mental rotation strategies in 210 normal subjects showed a strong tendency for right-handers to prefer rotating an object on the right and vice versa for left-handers. The differential functioning of the cerebral hemispheres during mental rotation was then assessed in 42 subjects by means of tachistoscopic presentation of two geometrical figures separately to the left and right visual fields--one of which was gravitationally stable and the other unstable. Performance was better when the unstable object was presented to the right visual field and the stable object to the left. This finding is interpreted as indicating more efficient hemispheric cooperation when the active manipulation of a mental image is performed by the left hemisphere, while the reference role is carried out by the right hemisphere.

Random-Number Generation and the Menstrual Cycle: Preliminary Evidence for a Premenstrual Alteration of Frontal Lobe Functioning

20 women (M age = 30.4 yr.) were given the “Mental Dice Task” (randomization of the numbers from 1 to 6) once during the preovulatory and once during the premenstrual phases of their menstrual cycles. In addition, for both test sessions a premenstrual-symptom score was assessed reflecting self-rated severity of cognitive, affective, and somatic complaints during the preovular and the premenstrual phases. In comparison to series of real dice throws, the Mental Dice sequences of all the subjects showed a relative lack of repetitions and an excess of counting at both times of testing. Counting bias was significantly enhanced in the sequences generated during the premenstrual testing and the size of this bias was positively correlated with the self-rated severity of premenstrual symptoms. Pronounced counting despite the instruction to randomize was interpreted as reflecting decreased ability to suppress task-irrelevant cues and indicating a relative impairment of frontal lobe functioning. Resistance of the Mental Dice Task towards expectation biases renders a sociopsychological interpretation of these results improbable. We conjecture that, like other cognitive processes, frontal lobe functions also fluctuate with hormonal changes.

The perception of harmonic triads: an fMRI study

We have undertaken an fMRI study of harmony perception in order to determine the relationship between the diatonic triads of Western harmony and brain activation. Subjects were 12 right-handed, male non-musicians. All stimuli consisted of two harmonic triads that did not contain dissonant intervals of 1 or 2 semitones, but differed between them by 0, ±1, ±2 or ±3 semitones and therefore differed in terms of their inherent stability (major and minor chords) or instability (diminished and augmented chords). These musical stimuli were chosen on the basis of a psychoacoustical model of triadic harmony that has previously been shown to explain the fundamental regularities of traditional harmony theory. The brain response to the chords could be distinguished within the right orbitofrontal cortex and cuneus/posterior cingulate gyrus. Moreover, the strongest hemodynamic responses were found for conditions of rising pitch leading from harmonic tension to modal resolution.

Lateralized Lexical Decisions and the Effects of Hemifield Masks: A Study of Interhemispheric Inhibition and Release

A lateralized tachistoscope experiment using 40 normal, right-handed men tested the predictions of three different theories of interhemispheric interactions. Lexical decision for function words was measured for each visual field under several conditions of simultaneous stimulation in the contralateral hemifield. When a nonsense word was presented simultaneously to the contralateral hemifield, performance decreased, especially for words in the weaker field, an effect which is inconsistent with the predictions of the direct access model. When the contralateral nonsense word was immediately masked, there was a significant improvement in performance over the nonmasked condition. Analysis of the masking effect showed that the data are inconsistent with a callosal relay model, but are consistent with a model of transcallosal inhibition.