Pigeons were trained on a multiple variable-interval/variable-interval schedule with pacing contingencies that generated high response rates in one component and low response rates in the other. Timeout periods separated the schedule components. During resistance-tochange tests, response-independent food was presented during the timeout periods, and the duration of that food presentation was varied among test sessions. Response rates in the schedule components decreased and latencies to the first response increased as a function of the duration of food presentations during the timeout. Both dependent measures changed about the same amount relative to their own baseline levels. The conclusions are that baseline response rates controlled by pacing contingencies are equally resistant to change, given equal reinforcement densities, and latency is a sensitive measure of resistance to change.
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...
After 3 groups of chickens had been reared in the dark, 1 group was maintained in the dark, 1 in monochromatic light of 589 m/u, and 1 in white light. After all groups were trained to peck a key in the presence of a 589-m/i light, a generalization test over wavelength was administered. All groups produced peaked generalization curves. No differences were found between the rearing groups. It was concluded that exposure to a continuum may not always be necessary to obtain a peaked generalization curve along that continuum.
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