An Empirical Test of Formal Equivalence between Emmert’s Law and the Size-Distance Invariance Hypothesis

Emmert’s law and the size-distance invariance hypothesis have been said to be formally equivalent, provided that Emmert’s law means that the perceived size of an afterimage is proportional to the perceived distance of the projected surface of the afterimage. However, there have been very few studies that have attempted to verify this formal equivalence empirically. We measured both the perceived size and distance of afterimages and real objects with the same proximal size. Nineteen participants projected afterimages of 1 deg in visual angle on the wall located at distances of 1 to 23 meters from the participants. They also observed real objects, disc-shaped and made from a sheet of Styrofoam board, with the same proximal size as that of the afterimages, which were located at the same physical distances as those of the wall on which the afterimages were projected. Each participant reproduced the apparent sizes of the afterimages and real objects using the reproduction method and estimated the apparent distances using the magnitude estimation method. When the mean apparent sizes of the afterimages and real objects, represented as a function of apparent distance, were fitted to a linear function, the slopes for the afterimages and real objects did not differ significantly. These results are interpreted as evidence for the formal equivalence of Emmert’s law and the size-distance invariance hypothesis.Es común considerar a la ley de Emmert y la hipótesis de la invarianza del tamaño-distancia como equivalentes formalmente. Para llegar a esta conclusión se parte de considerar que, al aplicar la ley de Emmert, el tamaño percibido de la postimagen es proporcional a la distancia percibida de la superficie en la que se proyecta. A pesar de lo anterior, muy pocos estudios han intentado verificar empíricamente esta equivalencia formal. En este trabajo se midió tanto el tamaño percibido como la distancia de postimágenes y de objetos reales con el mismo tamaño proximal. 19 participantes proyectaron postimágenes con un ángulo visual de 1 grado sobre una pared de 1 a 23 metros respecto a los participantes. Estos también observaron objetos reales, en forma de discos, hechos de una plancha de espuma Styrofoam, con el mismo tamaño proximal que el de las postimágenes, que se colocaron a las mismas distancias físicas que las de la pared sobre la que se proyectaron las postimágenes. Cada participante reprodujo los tamaños aparentes de las postimágenes y de los objetos reales usando el método de reproducción y estimó las distancias aparentes empleando el método de estimación de magnitudes. Cuando los tamaños medios aparentes de las postimágenes y de los objetos reales, representados en función de la distancia aparente, se ajustaron a una función lineal, las pendientes de las postimágenes y de los objetos reales no diferían significativamente. Estos resultados se interpretan como evidencia para la equivalencia formal de la ley de Emmert y la hipótesis de la invarianza del tamaño-distancia

Stereoscopic depth aftereffects without retinal position correspondence between adaptation and test stimuli

AbstractTo clarify whether stereo-slant aftereffects are independent of stimulated retinal position, two experiments compared the magnitude of aftereffects between the following two conditions: when the adaptation and test stimulus fell on (1) the same retinal position, and (2) on different retinal positions separated by 0.5°–20°. In Experiment 1, disc- or ring-shaped surface consisting of random-dots was presented at the central or peripheral visual fields. In Experiment 2, rectangular surface was presented at the upper or lower visual fields. After two minutes inspection of a random-dot stereogram depicting a ±30° slanted surface, the observer adjusted the slant of the test stimulus to appear fronto-parallel. The results of the experiments showed that significant aftereffects were observed similarly in both conditions. Moreover, the separation nor the stimulus shape scarcely affected the magnitude of the aftereffects. Based on these results we concluded that the depth processing mechanism which operates independently from the stimulated retinal position is responsible for the depth aftereffects we found

Attention shift not memory averaging reduces foveal bias

AbstractTwo experiments examined which of two mechanisms, attention shift or memory averaging, reduces foveal bias. The target stimulus was a black dot presented for 80ms while observers maintained fixation. The two main conditions were ‘with’ and ‘without’ vertical and horizontal bars as landmarks, which were placed on more eccentric positions than the target stimulus. To induce attention, the landmark was flashed on for 80 ms (Experiment 1) or disappeared (Experiment 2) with a stimulus onset asynchrony of 0, 106.4, or 212.8ms in both experiments. As a control, non-flashed and non-disappeared landmark conditions were employed. The observers’ task was to point to the remembered location of the target with a mouse cursor. The results showed that the magnitudes of foveal bias were significantly lower in the flashed and disappeared landmark conditions than in the without landmark condition. Furthermore, the magnitudes in the flashed and disappeared landmark conditions did not differ from their respective control conditions. The latter finding in the disappeared landmark conditions provides evidence for ‘attention shift’ against ‘memory averaging’ as the mechanism reducing foveal bias

The effect of directions of sound source on location of the auditory egocenter

The present study estimated the location of the origin of spatial coordinates in the human auditory localization system, which is called the auditory egocenter. A standard sound was presented from one of eight loudspeakers located at 30, 60, 120 and 150 degrees around the head. A loudspeaker for a comparison sound was moved by the experimenter on the arc at one of three distances of 30, 45 and 60cm from the head center, and the comparison sound was presented after the standard sound. Subjects\u27 task was to answer whether the perceived direction of the comparison sound was frontward or backward with respect to that of the standard sound. The results showed that: (a) when the standard sound was presented within the central visual field, the estimated auditory egocenter was very near the midpoint of the interocular axis, and (b) when the standard sound was presented in the peripheral or out of the visual field, it was very near the head center. The results indicate that location of the auditory egocenter is variable along the head median plane, depending on the direction of target sound with respect to the head