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R A Gregson

Publications and source records attributed to R A Gregson.

At least 19 recordsLinked to original sources
PubMed1992

Similarities of low-dimensional chaotic auditory attractor sequences to quasirandom noise.

The production of sequences of sounds of various pitch levels from the algebra of chaotic attractors' trajectories is relatively straightforward. Meyer-Kress (cited in Kaneko, 1986) suggested that such sequences would be distinguishable from random independent identically distributed sequences. In psychophysical terms, this is a pattern-discrimination or pattern-similarity perception task, but these two tasks are not exactly the same thing. Nine attractors from the algebras of Henon, Zaslavskii (1978), Kaplan and Yorke (1979), Lorenz, and Gregson, and the logistic and Baker transformations, were paired with 10 realizations of a random series. The identification of the random member in each pair, the confidence of identification, and the perceived pairwise similarity were recorded by 65 subjects without initial feedback and by 76 subjects with initial feedback on five trials only, for each of 20 such pairs. The results indicate varying degrees of discriminability; they can be expressed in an analog of the receiver-operating characteristics of the attractors. There is no evidence of any homogeneous basis for the discrimination, and subjects who perform better are apparently not using the same bases as those who perform poorly. The fractal dimensionality of attractors may furnish a basis for their recognition, or the consequent autoregressive spectra induced in finite (short) samples, but recent work suggests the latter spectra can be insensitive to low-dimensional attractor dynamics.

Adult↗
PubMed1990

Comparisons of the nonlinear dynamics of electroencephalograms under various task loading conditions: a preliminary report.

Comparison of the characteristics of electroencephalogram (EEG) records treated as realizations from a nonlinear process were compared under four different conditions: eyes shut resting, and three silent observation instructions to predict the patterns of randomly generated lights which illuminated every 10 seconds. The correlation dimension of the EEG was calculated by a method involving finding the correlation integral in m-dimensional space, and found to show some variations within time series. The degree and directions of changes in the dimensionality of the process varied between observers and did not clearly confirm some earlier reported findings, but it is demonstrable that the measures of nonlinear brain dynamics can be correlated with psychological variables. Reasons for this are discussed.

Adult↗
PubMed1990

The size-weight illusion in 2-D nonlinear psychophysics.

An extension of unidimensional nonlinear psychophysics is postulated by using forms of cross-coupling between the parameters of the two single-channel recursions, which have already been shown to model some perceptual phenomena. The size-weight illusion is shown to be reproducible in the topology of its relations, and it is suggested that some so-called illusions are in fact the natural consequences of nonlinear cross-coupling. The conditions that produce the illusion involve partially compensating the cross-coupling of sensory dimensions, and a second equilibrium with no cross-coupling, resembling simpler veridical perception, also exists in the behavior of some subjects.

Adult↗
PubMed1989

A nonlinear systems approach to Fechner's paradox.

It is possible to predict the topology of isointensity plots under conditions of extreme imbalance of the stimulus inputs, without making any assumptions specific to the circumstances in which Fechner's Paradox is sometimes observed. This is done by extending a nonlinear model for a sensory channel, by postulating a form of cross-coupling or interference between two channels which represents other phenomena in psychophysics. It is noted that the form in which data are usually reported is not an adequate basis for testing all the predictions of a nonlinear model in sensory psychophysics. The physiologist Panum (1958), and later Fechner (1860) reported that the apparent brightness of an object viewed binocularly could, under conditions where the input to one eye was diminished by filtering, be less than its brightness viewed monocularly by the unfiltered eye. To a first approximation, binocular brightness is more like an averaging of two monocular inputs than a summation of those same inputs. For over 120 years this phenomenon, which came to be called "Fechner's Paradox", though Panum should perhaps have had some credit, has been the subject of experimental investigation and associated mathematical modelling. If one consults a dictionary of psychological terms, for example Evans (1978), one may read something like Fechner's Paradox: The name give to the observation that something [which is] viewed binocularly seems to increase in brightness when one eye is closed. And yet we now know that this definition is misleading, because the same phenomenon in pooling two sensory inputs has its analogues in audition (Lehky 1983) and in olfaction (Gregson 1986). Gilchrist and McIver (1985) have now shown an analogue of the paradox exists in ocular contrast sensitivity. The definition also goes awry when the input luminance to one eye is zero, or when the luminance and ocular adaptation are closely matched for the two eyes. It is wiser, in the light of results reporting individual differences in the existence and extent of the paradox, and its sensitivity to stimulus conditions, to side with Blake and Fox (1973) when they observed that it is not unreasonable to suppose that various stimulus conditions might yield varying amounts of summation or even inhibition. Empirical reviews of relevant data in vision have been given by Roelofs and Zeeman (1914), Blake and Fox (1973), and Blake et al. (1981), but a theoretical model of interest as a starting point is that of Lehky (1983).

Computer Simulation↗
PubMed1985

Cross-modal identification: effects of contingent changes in the stimulus series.

Two computer controlled experiments in an olfactory cross-modal matching task, using two-component odour mixtures matched against bar diagrams, were designed so that stimulus presentation was contingent upon the recent performance of the subject; stimuli that were relatively poorly (in experiment 1) or well (in experiment 2) matched were more frequently presented. Analysis shows that the autoregressive structure of the performance is modified by such contingent presentation and that there is a weak relationship between transmitted information in matching and the time series structure of the matching errors. It is suggested that the process is nonlinear.

Adolescent↗
PubMed1981

Olfaction in Korsakoffs, alcoholics and normals.

Samples of 12 hospitalized Korsakoffs, 12 hospitalized non-Korsakoff alcoholics, and 12 controls, all groups being of comparable age range, were tested using a set of seven visual and olfactory measures which involved memory. By stepwise multiple discriminant analysis it was shown that strong separation could be effected between the three groups, solely on the basis of the olfactory recognition and recall tests, which included the Campbell-Gregson (1972) procedure. The use of of anosmia as a diagnostic indicator for Korsakoff's syndrome is discussed.

Adult↗
PubMed1979

Antarctic wintering--over, suggestion and transient olfactory stimulation: EEG evoked potential and electrodermal responses.

EEG evoked potential and electrodermal responses to real and suggested olfactory stimulation were recorded on a team of nine men who wintered-over at Scott Base, Antarctica. Multi-variate analysis of variance findings indicated some consistent trends despite adverse conditions and marked inter-individual differences. Consistent with studies of secondary afferentation olfaction-related EEGs were evidenced in the occipital area (O1 and O2) as well as the temporal area (T3 and T4). Skin conductance (SC) showed significant responses for real and suggested odorants pre and post wintering-over. Suppression of EEG amplitudes for real and suggested stimuli was evidenced prior to wintering-over. Following wintering-over experience suppression of EEG amplitudes for real stimuli showed a decrease while suppression increased for suggested stimuli. The implications of the suggestion findings are discussed in possible explanation of the apparent conflict between different sources of information about human responses to isolation in the Antarctic environment.

Alpha Rhythm↗
PubMed1977

Prediction of relapse in men alcoholics.

Cognitive impairment, as measured by the Patterned Cognitive Impairment Test, was the best predictor of relapse in a group of patients after treatment for alcoholism.

Alcoholics Anonymous↗