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PubMed1981

Form equivalence of the speech perception in noise (SPIN) test.

An evaluation was conducted of the equivalence of the ten forms of the Speech Perception in Noise (SPIN) Test with normal hearing subjects. Each subject was tested monaurally on all ten forms. Twenty-five subjects were presented the materials at 80 dB SPL at a signal-to-babble ratio of - 1 dB. An additional 25 subjects heard the materials at 30 dB SPL, at a signal-to-babble ratio of + 3 dB. The data were analyzed for equivalence using a parallel tests model. A detailed rationale for the application of this model to the equivalence of the SPIN test is presented. The results indicated that a subset of seven lists fits the equivalence model for PH, PL, and difference (PH - PL) scores. Additionally, analysis of list-pair data (combination of companion forms) suggested that all five list-pairs resulted in equivalent performance.

Adult↗
PubMed1994

[The history of research in color perception as a key to understanding various forms of congenital defects in red-green perception].

It is accurate to date the first scientific report about colour-deficiencies on 1777. Earlier descriptions may be followed up to the end of the 17th century. But usually it is only mentioned, that mistakes had happened. Huddart 1777, however, reported for the first time, that more than one person was involved in a family and that demonstrations of coloured ribbons helped to find out which colours became confounded. The famous self-observation of Dalton contains the assortment of individually combined silk-threads, which is an anticipation of subsequent arrangement-tests. Goethe developed a systematic arrangement-test of self-made small coloured targets with colours out of his own colour-wheel. A. Seebeck was the first who--using the spectrum for examination--found out that a special group of subjects showed a shortening of the spectrum at the red end. From this result Helmholtz concluded the existence of two types of red-green blindness. This new argument for the trichromatic organisation of our colourvision was the basis for the statement of the three types: protanopia, deuteranopia and tritanopia (v. Kries, A. König). Rayleigh later on succeeded in finding out anomalous trichromats following preparatory examinations of Maxwell. Nagel has the merit to have analysed protanomaly and deuteranomaly using the anomaloscope constructed by himself. Side by side with the spectral colour-tests pseudoisochromatic plates were developed for diagnostic purposes, at first thought out and introduced by Stilling and in the meantime used in many variations.

Color Perception Tests↗
PubMed2002

Transsaccadic memory of position and form.

Why and how people perceive the visual world as continuous and stable, despite the gross changes of its retinal projection that occur with each saccade, is one of the classic problems in perception. In the present paper, we argue that an important factor of visual stability and transsaccadic perception is formed by the reafferent visual information, i.e., the visual display that is present when the eyes land. After a review of some of the relevant theoretical, behavioural and physiological research on space constancy, saccadic suppression and transsaccadic memory, three experiments are presented. In a first experiment, we study the effect of an extended horizontal bar covering the target area for a short period after the saccade on saccadic suppression of image displacement. The results show that the bar acts just like a temporary blanking of the saccade target, leading to a strong reduction of saccadic suppression. In the second experiment, we show that any object that is present immediately after the saccade can establish a spatial reference, even if it is dissimilar to the saccade target. In a third experiment we study, with a similar approach, the effect of blanking and postsaccadic information on transsaccadic integration of form information. The data demonstrate that a localized postsaccadic object tends to replace the content of transsaccadic memory.

Form Perception↗
PubMed1989

Forms can be recognized from dynamic occlusion alone.

Direct and indirect theories of perception differ on whether form perception depends on higher order invariants or on features in the retinal image. The present paper describes a demonstration that an object can be recognized through a higher order pattern (dynamic occlusion) without any of the object's features being displayed. Stimuli consist of computer stimulations of black wireframe objects moving in front of, and occluding, a random layout of point lights on a black background. In this way, no single videoframe of the stimuli displays any of the object's features, and motion of the amodal object in front of the light points is necessary for the form to become visible. The forms can also be recognized when isoluminous colours are used for background and point lights. Finally, it is noted that, if the observer can actively control the motion of the object, e.g., by moving a computer mouse, recognition is enhanced as in Gibson's (1962) experiment on active touch.

Attention↗
PubMed1996

Spatial nonuniformities in visual search.

Previous search experiments in this laboratory have been concerned with the marked differences in target detectability as a function of its location in the visual field-differences we have called a detectability gradient-when subjects were required to detect a vertically oriented "target" among a number of distractor items having different orientations. This gradient was characterized by a marked right visual field superiority as well as differences in the shape of the gradient in the two half fields. A scanning model was proposed to account for these robust phenomena. The present experiments, using reaction time methods with vertical, horizontal, and colored targets have revealed marked differences in both reaction time and detectability as a function of target location and have isolated some of the spatial nonuniformities in the visual system which influence the shape of these gradients. The results reported here have forced us to abandon the scanning hypothesis in favor of a model in which attention is efficiently guided to the target.

Adult↗
PubMed1979

A quantitative study of chromatic organisation and receptive fields of cells in the lateral geniculate body of the rhesus monkey.

The responses of neurones in the lateral geniculate nucleus (LGN) were investigated in anaesthetised rhesus monkeys. A new classification for cells in the parvocellular layers (PCL) is proposed, based on their spectral response curve and their response to white stimuli: (A) narrow-band, short wavelength (NS) excited cells, activity suppressed by white stimuli; (B) wide-band, short-wavelength (WS) excited cells, excited by white stimuli; (C) wide-band, long-wavelength (WL) excited cells, (D) narrow-band, long-wavelength (NL) excited cells, activity suppressed by white stimuli; (E) light suppressed (LI) cells, activity suppressed by all wavelengths, usually with some concealed excitatory input at extreme short or long wavelengths. Responses to moving bars and to spots of various diameters (area response curves) were determined for various wavelengths. It was found that the receptive fields from which wavelength-dependent excitatory or suppressive effects could be elicited are concentrically superimposed. The spectral responsiveness of the excitatory inputs to individual cell types corresponds to the absorption curves of single cones (S-, M- or L-cone for NS, WS and WL cells respectively), the spectral distribution of the suppressive mechanisms of all cells was panchromatic and approximately fitted to a sum of all cones. The excitatory input to NL-cells cannot be related to any of the known cone absorption curves, and a simple (L-M) subtraction model is questioned. Neurones in the magnocellular layers (MCL) can be divided into on- and off-centre cells as in the cat's LGN and give qualitatively similar responses over the whole spectrum. In contrast to the tonic responses of PCL cells, MCL cells respond phasically to chromatic and white flashed spots, even with the smallest stimuli. Implications of these findings for colour processing in the LGN are discussed.

Animals↗