RESUMEN
The visual system can detect coherent motion in the midst of motion noise. This is accomplished with motion-sensitive channels, each of which is tuned to a limited range of motion directions. Our aim was to show how a single channel is affected by motions both within and outside its tuning range. We used a psychophysical reverse-correlation procedure. An array of dots moved coherently with a new, randomly chosen, direction every 14 or 28 ms. Human subjects pressed a key whenever they saw upwards movement. The results were analyzed by finding two motion directions before each key-press: the first preceded the key-press by the reaction time, and the second preceded the first by a variable interval. There were two main findings. First, the subject was significantly more likely to press the key when the vector average of the two motions was in the target direction. This effect was short-lived: it was only seen for inter-stimulus intervals of several tens of milliseconds. Second, motion detection was reduced when the target direction was preceded by a motion of similar direction 100-200 ms earlier. The results support the idea that a motion-sensitive channel sums sub-optimal inputs, and is suppressed by similar motion in the long term.
Asunto(s)
Percepción de Movimiento/fisiología , Estimulación Luminosa/métodos , Percepción Visual/fisiología , Adulto , Distribución de Chi-Cuadrado , Femenino , Humanos , Masculino , Modelos Psicológicos , Psicofísica/métodos , Tiempo de Reacción , Percepción Espacial/fisiología , Factores de TiempoRESUMEN
Motion provides important cues for the perception of depth and object structure. The kinetic depth effect illustrates this phenomenon: dots moving in a two-dimensional plane can produce a vivid perception of a rotating three-dimensional object. We studied the origin of this depth percept in a psychophysical study employing inducing and test stimuli. The inducing stimulus, containing dots moving with simple harmonic motion in the fixation plane, was perceived as a rotating cylinder. The test stimulus had binocular disparity that placed it close to either the near or far surface of the cylinder. We found that sensitivity to the test was lower when it moved in the opposite direction to the adjacent surface of the inducing stimulus than when the two stimuli moved in the same direction. We also simplified the inducing stimulus by using two uniform arrays of dots translating in opposite directions. Subjects saw one array as being closer than the other, and test sensitivity was again reduced when the test was close to a surface moving in the opposite direction. These results support the idea that there are suppressive interactions between opposing motions at the same depth, leading to a single perceived direction of motion at each depth.