RESUMEN
Two experiments on figure-ground organization were designed to examine whether the regions of an ambiguous stimulus perceived as "figure" vary as a function of regional area and experience with the stimulus. In Exp. 1 the perceived duration of each interpretation was recorded during continuous viewing for 10 subjects who had been trained until both percepts appeared with statistical regularity (stationary phase). In Exp. 2 the first interpretation reported by 172 naive observers after a few seconds of pattern exposure was recorded. The well-known tendency to interpret smaller regions as figure was noted in Exp. 2 whereas the results of Exp. 1 suggested equal probability of the percepts. Over-all results suggest that alternation is learned during the transient or "early" phase of perception, with some stimulus features and cultural factors influencing the figure-ground organization. During the stationary or late phase of perception the subject is well practiced and the alternating of interpretations becomes largely automatic.
Asunto(s)
Atención , Aprendizaje Discriminativo , Área de Dependencia-Independencia , Reconocimiento Visual de Modelos , Adulto , Femenino , Humanos , Masculino , Ilusiones Ópticas , Orientación , PsicofísicaRESUMEN
To study the influence of eye movements on the time course of perceptual alternation of ambiguous patterns, we recorded the reversal signals and eye movements of four subjects, during prolonged observations of a Necker cube, under three experimental conditions: unrestricted normal viewing, instruction-restricted normal viewing, and imperfectly stabilized viewing. An important decrease in the frequency of saccadic eye movements and a significant increase in the reversal rates were shown by all subjects under imperfectly stabilized viewing over the normal unrestricted viewing. Moreover, three out of four subjects showed a significant decrease in their reversal rates when changing from the normal to instruction-restricted viewing. Results are discussed in terms of the role and time cost of scanning eye movements in perceptual processes.
Asunto(s)
Atención , Aprendizaje Discriminativo , Movimientos Oculares , Percepción de Forma , Ilusiones , Ilusiones Ópticas , Reconocimiento Visual de Modelos , Adulto , Fijación Ocular , Humanos , Orientación , PsicofísicaRESUMEN
In this work, the results of two experiments on ambiguous patterns are reported, which have been obtained by presenting a series of stimuli designed, in both cases, to reduce gradually the ambiguity of the patterns. Such reduction has been performed by respectively increasing or decreasing the amount of graphic details in the experiments. Data of both experiments show a lengthening of mean reversal time. The increase in the stability of one percept can be regarded as associated with the increasing difficulties encountered by an observer in organizing and restating the alternative "hypothesis" through the perceptual mechanisms. The loss of balance in the durations of percepts is discussed in terms of their different informational contents. Finally, in Exp. 1 an analysis is made to evaluate to what extent an addition of perceptual cues, designed to reinforce a three-dimensional interpretation of a pattern, can influence its figure-ground alternation.
Asunto(s)
Aprendizaje Discriminativo , Percepción de Forma , Ilusiones , Ilusiones Ópticas , Reconocimiento Visual de Modelos , Disposición en Psicología , Adulto , Atención , Percepción de Profundidad , Femenino , Fijación Ocular , Humanos , MasculinoRESUMEN
Reversal rates of an ambiguous figure (the Necker cube) were studied for different pattern sizes covering a range of visual angles theta from approximately 1 to 62 deg. A large number of reversals was obtained for each observer and each pattern in order to examine the statistical distributions of reversal times. A pronounced flattening of the statistical distributions (represented throughout by a gamma distribution) and a growth of the mean duration of each percept, with increasing pattern size was found. A plateau in the range of theta between 5 and 20-30 deg was observed. For larger values of theta two kinds of observers have been identified: for 'fast' observers the inversion rate is little affected by theta, whilst for 'slow' observers, the mean reversal time increases strongly with theta. A tentative model, based on three different contributions to the duration of the alternation process, is proposed: a constant term, independent of theta, and two terms dependent on theta--a retinal term, and a cortical one. The last term is interpreted as due to the spreading of excitation with the characteristic of a filling-in process.