The effects of outward-pointing arrowheads on the Mueller-Lyer illusion in pigeons

Abstract

In an earlier analysis of the Mueller-Lyer illusion in pigeons it was found that when birds trained with flat-vertical An illusion is defined as the condition in which the point of subjective equality (PSE) does not equal the point of objective equality (POE). Thus, in studying illusions in animals one could say that an illusion has occurred if the peak of a generalization gradient (PSE) does not equal the value of the training stimulus (Malott, 1967).In an analysis of the Mueller-Lyer illusion using pigeons, the Sa were trained to peck a key when a 1.3 cm horizontal line with flat-vertical arrowheads on each end of it was projected on the response key (Malott & Malott, 1967). The birds were not reinforced for responding when the key was dark. During generalization testing, half of the birds were tested with 90 0 arrowheads (inward-pointing) and the other half with 270 0 arrowheads (outward-pointing) on each end of the line. Curves from tests with inward-pointing arrowheads were more or less like the curves with flat-vertical arrowheads. Peaks were at the training value. If there were any differences at all, the gradients with the inward-pointing arrowheads were more variable and broader. The tests with the outward-pointing arrowheads showed an increase in response rate as the length of the test line was increased. However, the gradients did not peak. It was hypothesized that the effect of the illusion was great enough to cause the peaks to shift outside the range of test stimuli used. The present experiment was designed to test this hypothesis by using a shorter training stimulus and, thus, increasing the upper range of the test stimuli. MethodThe Sa were six experimentally naive white Carneaux barren hen pigeons. They were maintained at 70% of their free-feeding body weight.The response key was transillwninated by a projector. An example of the training stimulus (8+) is shown on the left side of Fig. 1. The horizontal line was 0.7 cm and the flat-vertical arrowheads on each end were 0.7 cm.Psychon. Sci., 1967, Vol. 9 (I) After initial shaping in the presence of the 8+, the birds were reinforced for every response when the 8+ was on the key. No responses were reinforced when the key was dark (S-). The stimulus was terminated after every reinforcement and stayed off for 30 sec of no responding. That is, a response during the 30 sec Speriod caused the 30 sec interval to recycle. Thus, the 8+ was only presented after 30 sec had elapsed without a response while the key was dark.The reinforcement requirements in the presence of the S+ were gradually increased until the pigeons were responding on a random-interval schedule of 64 sec (RI64-sec) (cf., Farmer, 1963).After 15 days of training on the RI64-sec schedule, each pigeon was given a generalization test over various lengths of line which had outward-pointing arrowheads (270 0 ) on each end. This type of stimulus is shown on the right side of Fig. 1. The length of each side of each arrowhead was .35 cm. The pigeons then received a second test after another week...

Experimental Divergences in the Visual Cognition of Birds and Mammals

“…Because of these considerations, the examination of visual illusions in animals has been of long-standing interest (Fujita, Nakamura, Sakai, Watanabe, & Ushitani, 2012; Malott, Malott, & Pokrzywinski, 1967; Révész, 1924; Warden & Baar, 1929). If animals experience visual illusions as we do, it would be good evidence that the underlying processes and representations are functionally the same, since illusions directly capture the influence and action of neural processes.…”

Do pigeons perceive the motion aftereffect? A behavioral study

“…It therefore accords with the electrophysiological results of Niu et al [35] which identified a cellular correlation of the MAE at midbrain level in pigeons. As we know, the birds can perceive geometric illusions in static displays (pigeon [19,20,22,30,31]) as well as illusory contours defined by contrast gradients (pigeon [35]; barn owl [34]; chick [47,53]). The present study extents this list for the first time to the domain of movement illusions.…”

“…Three studies had addressed the Müller-Lyer illusion using pigeons and revealed a similar pattern of perception as humans as long as inward arrows were used [20,30,31]. Further evidence [19] showed that the performance of pigeons in discriminating the length of bars located between converging contexts (Ponzo illusion) was affected by the context direction.…”

“…Most illusion studies were conducted on human subjects [14,49] and mammals [5,6,8,[11][12][13]18,25,40,45,54] not birds. And all of these experiments done on birds utilized static patterns such as the Müller-Lyer, Ponzo or subjective contour illusions (pigeons [19,20,22,30,31]; barn owls [34]; chick [47,53]). In addition, chicks were shown to achieve relative depth disambiguation [15] and amodal completion [39].…”

Perception and Stimulus Generalization

“…Subsequent generalization tests produced statistical evidence for matching behavior (Malott et al, 1967b). However, we would prefer to have stronger evidence than was shown before closing the question of whether matching behavior may be reliably obtained without discrimination training.…”