K. Geoffrey White

Parallel-serial processing and hemispheric function

Abstract In one experiment 14 subjects made same-different responses to geometric forms varying in number from two to four, and presented randomly in the left or right visual hemifields. In a second experiment two different groups of subjects ( N 1 = N 2 = 6) responded to letters, varying in number from two to four which could be matched on either nominal or physical identity. In both experiments reaction times were faster for stimuli directed to the right hemisphere and in no condition did reaction times increase with increasing number of stimuli. Implications for a relationship between mode of processing and hemispheric function were discussed.

On the Relation Between Productivity and Impact

The number of publications per person per year and the number of citations to published work per person per year were counted for a sample of 299 Australasian academic psychologists for the period 1970–1975. Ten per cent of the sample accounted for 36% of the publications and 10% of the sample for 60% of the citations. At the level of universities there was a relationship (r = .70) between productivity (publications) and impact (citations). Across the 242 individuals with at least one publication, there was no productivity-impact relationship (r = .10).

Stimulus presentation frequency in brightness discrimination and generalization: A test of adaptation-level and signal-detection interpretations

In Experiment 1, brightness discriminations were established under conditions in which the stimulus to which “same” responses were required (S+) was presented more frequently than the stimulus to which “different” responses were made (S−), S+ and S− were presented equally often, or S− was more frequent than S+. Subsequent generalization gradients along the brightness dimension were shifted away from the stimulus value more frequently presented during training. In Experiment 2, brightness discriminations were established under conditions of equally frequent presentations of S+ and S− stimuli in training, but in subsequent generalization testing S+ and S− values were equally represented or overrepresented relative to presentations of other test stimuli. Generalization gradients shifted towards the overrepresented stimulus value, relative to gradients obtained for equal presentation-frequency conditions. The shift in gradients away from the more frequently presented stimulus during training in Experiment 1 was consistent with accounts of stimulus generalization based on both adaptation-level theory and signal-detection theory. The shift in gradients towards the more frequently presented stimulus during testing in Experiment 2, however, was consistent with adaptation-level theory, whereas the signal-detection account had predicted a shift in the opposite direction. These results attest to the importance of relative stimulus presentation frequency as a determinant of postdiscrimination stimulus generalization performance. Because feedback was given only during training, the opposite effects of presentation probability in training and testing may reflect an interaction between presentation probability and feedback.

Responding in the presence of free food: Differential exposure to the reinforcement source

Preference in rats for response-contingent reinforcement vs free food was studied as a function of differential exposure to the response-contingent and free reinforcement sources. Subjects trained primarily with response-contingent reinforcement exhibited responding for food in the presence of free food in later preference tests, and allocated more time to the response-contingent reinforcement source than did subjects trained with equal exposure to the reinforcement sources. Subjects trained to take freely available food did not respond in the presence of free food. The phenomenon of responding for food in the presence of free food was thereby demonstrated to be a consequence of prior operant or instrumental training.

Stimulus control of topographically tagged responding

Pigeons’ responses on an operant key were reinforced according to either multiple variable-interval variable-interval or multiple variable-interval extinction schedules. The multiple-schedule components were signaled by line-tilt stimuli on a second key (signal key). Signal-key responses never produced reinforcement, and operant-key responses were not reinforced if they followed within 1 sec of a signal-key response. Behavioral contrast was not observed on the operant key, although there was a small, but reliable, increase in signal-key responding in the variable-interval component of the multiple variable-interval extinction condition. Generalization tests were interspersed between sessions of multiple variable-interval extinction training. Generalization gradients along the line-tilt dimension exhibited peak shift for both operant-key and signal-key responding following intradimensional (line tilt) discrimination training. Line-tilt generalization gradients following interdimensional discrimination did not exhibit peak shift. Gradients following intradimensional discrimination were sharper than gradients following interdimensional discrimination for both operant-key and signal-key responding. It was concluded that dimensional stimulus control of topographically tagged responding maintained by the stimulusreinforcer relation parallels that maintained by the response-reinforcer relation.

A note on the measurement of stimulus discriminability in conditional discriminations

In a conditional discrimination, pigeons’ responses on a right key were reinforced in the presence of a 0° line orientation, and responses on a left key were reinforced in the presence of any of five other orientations, 15° through 75°. Variable-interval schedules of reinforcement for right and left responses were changed over five experimental conditions. Values for a measure of discriminability of 0° from other orientations increased as orientation difference increased. Sensitivity of the choice between right and left in the different orientations, to reinforcers for right and left responses, changed with orientation difference. The effect of reinforcers in one component of a conditional discrimination on responding in another may therefore be modulated by the discriminability of the stimuli signaling the components.

Recognition memoryfor pictorial events

Subjects viewed sequences of slides depicting everyday events, and in later recognition tests, they correctly rejected distractors that were inconsistent with some invariant of the event but falsely accepted consistent distractors. J. J. Jenkins has accounted for the differential recognition of consistent and inconsistent slides of pictorial sequences in terms of fusion, the abstraction of an event from a series of temporally related items. The conditions under which event fusion was likely to occur were manipulated in three experiments: degree of ordering of the action-sequence slides, semantic vs. nonsemantic orienting tasks during acquisition, and duration of retention interval Recognition performance was generally more accurate under conditions of semantic processing, ordered acquisition sequences (for the semantic task), and shorter retention intervals. However, these variables did not affect differential recognition of consistent vs. inconsistent slides. A further experiment showed that the absence of an effect of disordering acquisition sequences on differential recognition could not be attributed to subjects’ reordering the disordered sequences in a way consistent with the original event. The data did not support the hypothesis that recognition performance was based on fusion of events depicted by temporally ordered slide sequences. It was suggested that memory for featural detail is a relevant factor in performance.

Postdiscrimination generalization as a function of interresponse time

Following 20 sessions of variable-interval 20-sec reinforcement in the presence of a single 45-deg line-tilt stimulus, three pigeons were trained to discriminate between line tilts of 45 deg correlated with variable-interval 20-sec reinforcement and line tilts of 15 deg correlated with extinction. A generalization test along the line-tilt dimension was administered following a criterion discrimination performance. Gradients derived in terms of relative frequency of response as a function of line tilt indicated strong external stimulus control and exhibited clear peak shift. From the interresponse time (IRT) distributions generated for responding to each test stimulus, probability of response conditional upon IRT (IRTs/Op) was derived as a joint function of line tilt and IRT. The IRTs/Op functions for responses following IRTs in 0.2-sec-wide classes from 0.2 to 1.0 sec and for responses following IRTs in the interval of 1.0 to 2.0 sec were similar to the relative generalization gradients and also exhibited peak shift. Few IRTs were greater than 2.0 sec. External stimulus control was established over responses terminating IRTs both longer and shorter than 1.0 sec.

Preference for response-contingent vs. free reinforcement

Preference in rats for response-contingent reinforcement vs. free reinforcement was examined by manipulating the rate of free reinforcement relative to the rate of response-contingent reinforcement in concurrent variable-interval variable-time schedules. Preference was assessed in terms of the time allocated to the alternative reinforcement sources independently of the differential reinforcement distribution, and was shown to be equal for response-contingent and free reinforcement.

Cerebral hemispheres serve as two channels for visual information processing

Grid patterns or CVC trigrams were presented tachistoscopically in the left or right visual fields or concurrently in both visual fields. There were fewer errors in identifying both grids and CVCs when a grid on the left was paired with a CVC on the right than when a CVC on the left was paired with a grid on the right. The result indicated that when each hemisphere received the type of stimulus material, spatial or verbal, for which its function was specialized, they served as separate channels and processing accuracy was maximal.