Signal probability and spatial location as possible bases for increased selectivity in noise

It was previously found that noise increased both performance on a primary tracking task and the detection of centrally located signals in a secondary multi-source monitoring task. The present experiment examines the effect of changing the distribution of signals across the monitoring display. When equal numbers are seen at all locations there is no differential effect of noise for central and peripheral locations. Such an effect only occurs when central signals are seen to have greater probability. This result points to the selectivity effect in noise being a function of task priorities and not of physical location.     

Visual on- and off-latencies and handedness

Ten Ss served in this experiment, five right-handed and five left-handed. Every S was tested in a perceived-order situation and by the up-and-down method to determine the relative on-latency for a visual test stimulus. i.e, (ON-Lat for lest stimulus involving right hemisphere- ON-Lat for standard stimulus involving left hemisphere) and to determine a similarly defined relative off-latency for the same test stimulus. The algebraic difference between the relative on-latency measure and the relative off-latency measure was then found. Data from a previous study had suggested that this “on-off difference” was characteristically positive for left-handed Ss and negative for right-handed Ss. The present data agree. The left-handed Ss were found to differ significantly from the right-handed Ss in the magnitude of the on-off difference. This outcome appears important as a possible clue to functional interhemispheric differences related to handedness.     

Selective eye movements to simultaneously presented stimuli during discrimination

Human Ss, when given a discrimination task whose stimuli varied in dimension and relevance, always chose and ftxated more frequently the stimulus they had been reinforced for choosing. Decreasing the brightness reduced the choice and ftxation preference for form stimuli over line stimuli and raised total ftxation frequency. Ss decreased fixation frequency to discriminanda with practice.     

The response-reinforcement dependency in fixed-interval schedules of reinforcement

Pigeons were exposed to four different schedules of food reinforcement that arranged a fixed minimum time interval between reinforcements (60 sec or 300 sec). The first was a standard fixed-interval schedule. The second was a schedule in which food was presented automatically at the end of the fixed time interval as long as a response had occurred earlier. The third and fourth schedules were identical to the first two except that the first response after reinforcement changed the color on the key. When the schedule required a peck after the interval elapsed, the response pattern consisted of a pause after reinforcement followed by responding at a high rate until reinforcement. When a response was not required after the termination of the interval, the pattern consisted of a pause after reinforcement, followed by responses and then by a subsequent pause until reinforcement. Having the first response after reinforcement change the color on the key had little effect on performance. Post-reinforcement pause duration varied with the minimum interreinforcement interval but was unaffected by whether or not a response was required after the interval elapsed.     

Effects of rate of reinforcement-time upon concurrent operant performance

Three experiments were conducted to investigate the theoretical reduction of rate and duration of reinforcement to their product, rate of reinforcement-time, under concurrent chain schedules. In Exp. I, rate of reinforcement-time was varied by varying rate of reinforcement delivery, holding duration of reinforcement availability constant; in Exp. II, rate of reinforcement-time was varied by holding rate of reinforcement delivery constant and varying duration of reinforcement availability; in Exp. III, rate of reinforcement-time was held constant by varying both rate and duration of reinforcement simultaneously and inversely. For all three experiments, both relative rate of responding and relative time spent in the initial link were found to match approximately the relative rate of reinforcement-time arranged in the terminal link. These data were interpreted as support for the notion that rate and duration of reinforcement may be functionally equivalent and reducible to a single variable, rate of reinforcement-time.     

The effect of a fading procedure upon the acquisition of control by an overshadowed auditory feature

Pigeons' key-pecking responses were reinforced in the presence of a compound stimulus that consisted of an auditory feature (a tone) and a visual feature (a light) and non-reinforced in the presence of a compound stimulus that was either a noise and a dark key, or noise and a light. In the condition where reinforcement trials differed from non-reinforcement trials on the basis of both auditory and visual features, the tone exerted very little control over responding on test. In the condition where reinforcement differed from non-reinforcement trials solely on the basis of the auditory features, an abrupt and a gradual introduction of the visual feature of the negative stimulus, a light, were compared for their effect upon control in the compounds. The tone acquired strong control in both cases. Evidence indicated that the tone had acquired control in the gradual condition without the occurrence of responses to the negative stimulus. An incidental finding was that when the negative stimulus consisted of a noise and a light, which was introduced abruptly, responding over the light dimension with tone, on test, was peaked at a point other than that light value used as positive and negative during training.     

Free-operant avoidance in the pigeon using a treadle response

A free-operant avoidance schedule was used to establish and maintain foot-treadle responding by two Homing, one White King, and two Carneaux pigeons. In the absence of responding, the interval between shocks equaled 10 sec. Each time a treadle response occurred the shock was postponed for 32 sec. Pigeons appear to learn the treadle response more quickly and use it to avoid shock more successfully than do rats bar pressing on similar schedules. The treadle response becomes highly stereotyped and interresponse time distributions obtained from terminal behavior appear very similar to data obtained from rats. It is concluded that the difficulty in training pigeons to avoid electric shock is not in establishing avoidance behavior but in attempting to evaluate such behavior with the key-peck response.