Perception

The problem discussed is the relationship between the firing of single neurons in sensory pathways and subjectively experienced sensations. The conclusions are formulated as the following five dogmas:

To understand nervous function one needs to look at interactions at a cellular level, rather than either a more macroscopic or microscopic level, because behaviour depends upon the organized pattern of these intercellular interactions.

The development of the concepts leading up to these speculative dogmas, their experimental basis, and some of their limitations are discussed.

When given a choice between two visual stimuli (plain fields of light of different colour, photographs, cine films, etc.) monkeys show strong and consistent preferences. The strength and direction of the preferences is determined by two independent factors: the monkey's relative ‘interest’ in the stimuli (determined largely by their information content) and his relative ‘pleasure’ (determined by qualities such as colour and brightness). With an unchanging stimulus ‘interest’ rapidly fades but ‘pleasure’ (or ‘unpleasure’) remains stable. If the two factors are set against each other, as when a red-coloured cine film is paired with a plain white field (the pictorial content of the film being interesting, its colour unpleasant), interest over-rides pleasure in determining the observed preference. A quantitative model based on these principles predicts the behaviour in a variety of situations with great accuracy.

A sample of Me'en (Mekan) drawn from a population having minimal contact with pictorial materials was found to be able to recognise correctly, albeit gradually and with a degree of effort, clearly depicted animals. They did make however some responses which in the west would be considered anomalous, and appeared to find the task stressful.

Un premier groupe de 58 enfants d'âge scolaire adressés à un service spécialisé dans le traîtement des troubles de la psychomotricité et du langage a été soumis a une série d'investigations ophtalmologiques, cliniques et EEG. Ces sujets ont été comparés à un deuxième groupe de 45 enfants strabiques de même âge, adressés à un département d'ophtalmologie, et soumis aux mêmes examens cliniques et EEG.

Parmi les sujets du premier groupe, 43% se sont révélés avoir des troubles de la fonction binoculaire; parmi les enfants du deuxième groupe (sans vision binoculaire), la proportion de troubles psychomoteurs et cognitifs importants n'atteint que le tiers de sa valeur dans le premier groupe.

L'analyse EEG des deux groupes a été faite par rapport à la qualité de la vision binoculaire, au degré de perturbation clinique et à l'anamnèse. Cette analyse montre: une nette relation entre foyers occipitaux de pointes et trouble (ou absence) de la vision binoculaire; entre désorganisation spatio-temporelle du rythme de fond, degré de perturbation clinique et anamnèse chargée. Les inter-relations entre perturbations de la fonction binoculaire, développement cognitif et EEG sont discutées et quelques conséquences pratiques de cette étude sont ébauchées.

Dans une expérience de masquage latéral, on étudie les modifications de l'intensité apparente d'un stimulus lumineux lorsqu'il est suivi ou précédé d'un stimulus masquant voisin. Les facteurs expérimentaux sont: (i) le délai Δt entre les deux stimulus (axe des abscisses sur les graphes) et (ii) l'écart spatial entre les stimulus. Les variations de la brillance (estimée sur une échelle d'intervalle en 9 points) sont analysées par rapport à la valeur de référence (V.R.: estimation du stimulus-test présenté seul). On obtient un effet de diminution de brillance lorsque les deux stimulus (test et masquant) sont proches à la fois dans le temps et dans l'espace (délai inférieur à 50 ms et écart inférieur à 10 minutes d'angle). Si l'écart spatial est augmenté (entre 0 et 10′), cet effet de masquage est atténué; cette atténuation est importante surtout en situation rétroactive contrairement à l'atténuation obtenue par d'autres facteurs (diminution d'énergie du stimulus masquant ou bien séparation dichoptique). On obtient un effet d'augmentation de brillance lorsqu'un intervalle, temporel ou spatial, est augmenté: le maximum étant obtenu lorsque le stimulus-test suit le stimulus inducteur (situation proactive), pour les délais de 75–150 ms. Ces résultats sont discutés en fonction des données obtenues dans d'autres travaux analysant les effets d'inhibition et de facilitation dans des expériences d'interaction spatiale ou temporelle.

Movement aftereffects contingent on colour and pattern (CMAEs) were produced. A pattern, illuminated with red light and rotating clockwise, was alternated with its contrast-reversed ‘negative’, illuminated with green light and rotating counterclockwise. Subsequently, when the stationary patterns were presented, subjects reported counterclockwise MAEs on the ‘red’ pattern, and clockwise MAEs on the ‘green’ pattern. It was found that a simple MAE produced by adapting to the ‘red’ pattern and tested on the ‘green’ pattern was greater in duration when the direction of the inducing motion was opposite to that used in the CMAE adaptation procedure. It is suggested that this directional asymmetry in the duration of the simple MAE may be used as a within-subjects measure of the CMAE.

A flow procedure was used to measure the sensitivity of two subjects to NaCl stimuli after adaptation to 10 mM and 30 mM NaCl. The signal detection rating procedure was used and thirteen receiver operating characteristic (R.O.C.) curves obtained. Assumptions of normality and equal variance for the noise and signal plus noise distributions were upheld while d′ and nonparametric P(A) values were found to be comparable to those reported in earlier threshold studies. Advantages of the technique are discussed.

Four different types of hearing were investigated using 25 men and 25 women as subjects: pure tone threshold, judgment of loudness, pitch discrimination, and annoyance of a repeating stimulus.

Differences were found at high frequency thresholds (above 6000 Hz), in loudness judgment, and in the annoyance test. The pitch discrimination test showed no effect of sex, but a large effect of years of musical training. None of the four hearing parameters investigated bore any statistical relationship to any other, demonstrating that these hearing types are distinct and will vary within, as well as between subjects. Personality assessment showed no relationship to any type of-hearing, with the exception of extraversion and loudness judgment, suggesting that fairly pure sensitivity factors are being measured.

Given a striped pattern, there are two ways of obtaining a phenomenal rarefaction of it: (a) by reducing the area of the pattern, leaving the distance between the stripes unchanged, or (b) by placing the pattern within one of Delboeuf's illusion contexts. With (a) phenomenal rarefaction is coupled with an increment of visual acuity, since the stripes are distinctly seen at a greater distance. With (b) the phenomenal rarefaction is the same as with (a), but is not associated with any increase of visual acuity. The rôle of ‘actual’ and ‘illusory’ conditions on visual perception is discussed.

Interocular transfer of the tilt aftereffect was investigated in normal humans with good stereopsis and in subjects without stereoscopic vision. These latter subjects were divided into two groups: those with and those without a history of strabismus. Strabismic subjects showed grossly reduced interocular transfer of the effect (12% mean transfer). Nonstrabismic subjects had moderate transfer (49%) and normal subjects showed approximately 70% mean transfer. All normal subjects showed greater transfer from the dominant eye to the nondominant than vice versa.

The results are discussed with respect to developmental effects in the visual system of cats and humans, and the nature of the tilt aftereffect.