Temporal discrimination factors in the delayed matching-to-sample task in monkeys

The temporal discrimination hypothesis (TDH) of delayed matching-to-sample (DMTS) stresses the animal’s ability to discriminate which choice-stimulus alternative has appeared most recently as sample. Thus, the emphasis is placed on discriminative processes, temporal in nature, rather than on the traditional trace or buffer storage mechanisms of short-term memory. Some of the predictions of the TDH were tested within the context of the DMTS task. Experiment I showed that the difficulty of sample-stimulus sequences could be predicted by the TDH. Experiment II showed DMTS performance to be an increasing function of the number of sample stimuli employed, a result predicted by the TDH, but not by a traditional proactive interference interpretation. The results demonstrate the importance of temporal discriminative processes in DMTS. The possibility for a simpler theoretical approach to memory, in general, is discussed.

     

Within-session changes in responding during delayed matching-to-sample and discrimination procedures

Two experiments examined within-session changes in responding during discrimination procedures. In Experiment 1, rate of responding changed significantly within sessions during symbolic delayed matching-to-sample tasks when the delay between the stimulus and the choice period was short (1–5 sec), but not when it was long (8–12 sec). The percentage of responses that were correct did not change within sessions. In Experiment 2, response rates increased and then decreased within sessions during both S1 and S2 when successive discrimination procedures provided high, but not low, rates of reinforcement. Discrimination ratios sometimes increased within sessions. These results question two potential definitions of attention as explanations for within-session changes in response rates. They are more compatible with explanations based on concepts such as arousal, satiation, habituation, and interfering responses.     

Remembering as discrimination in delayed matching to sample: Discriminability and bias

Task difficulty in delayed matching-to-sample tasks (DMTS) is increased by increasing the length of a retention interval. When tasks become more difficult, choice behavior becomes more susceptible to bias produced by unequal reinforcer ratios. Delaying reinforcement from choice behavior also increases both task difficulty and the biasing effect of unequal reinforcer probability. Six pigeons completed nine DMTS conditions with retention intervals of 0, 2, 4, 6, and 8 sec, in which reinforcer delays of 0, 2, and 4 sec were combined with ratios of reinforcer probabilities of .5/.5, .2/.8, and .8/.2 for correct red and green responses. Discriminability (logd) decreased with both increasing retention interval duration and increasing reinforcer delay. Sensitivity to reinforcement, the tendency for ratios of choice responses to follow unequal reinforcer probabilities, also increased as a function of both increasing retention interval and increasing reinforcer delay. The result is consistent with the view that remembering in DMTS tasks is a discriminated operant in which increasing task difficulty increases sensitivity to reinforcement.     

The role of within-trial location of the retention interval in rats’ delayed conditional discrimination performance

Rats were trained and tested on delayed conditional discriminations (DCDs) consisting of four possible light and tone stimulus sequences: light-light, tone-tone, light-tone, and tone-light. A lever was presented after the offset of the second or test stimulus, S₂. Two retention intervals (RIs) were present within the DCD task, one (RI-1) between the sample or first stimulus (S₁) and S₂, and the other (RI-2) between S₂ and presentation of the lever. Liquid reinforcement was contingent upon pressing only when S₂ matched S₁ in Experiment 1 or only when S₂ differed from S₁ in Experiment 2. RI-1 and RI-2 were separately increased to 5,10, and 20 sec from 1-sec training conditions. Increasing RI-1 produced greater declines in performance to light S₁ than to tone S₁ in both experiments. No such stimulus modality effect occurred for increases in RI-2 in these experiments. These results indicate that retrospection of S₁ occurred during RI-1 and prospection of a response decision and reward expectancy primarily occurred during RI-2.     

An analysis of positive general transfer in discrimination learning in the rat

As a result of learning a single discrimination problem, rats and pigeons will show positive transfer to totally new discriminations. It has been suggested that this transfer effect reflects the development of a process of general attentiveness. However, alternative explanations of the transfer effect are available which do not require any radical departure from traditional discrimination learning theory. The three experiments reported here demonstrate positive general transfer in rats trained on a simultaneous discrimination and tested under conditions which rule out these alternative explanations. The experiments also attempt to specify the nature of the processes underlying the general transfer effect.     

“Thinking ahead” in rat discrimination learning

If rats chose S+ in a brightness discrimination in a T-maze, they experienced, on that run and over four forced runs to S+ which followed, a pattern of reinforcement in which quantity of reward in the goalbox increased from 0 to 14 food pellets, decreased from 14 to 0 food pellets, or varied randomly. If the rats erred and chose S?, reinforcement was withheld, and they were forced a second time to 0 reward in the S? goalbox. The results indicate that rats readily learn the brightness discrimination under these conditions, the animals exposed to the sequentially increasing pattern learning somewhat slower than the others. This was true in spite of substantial delay of reward. Theoretical accounts based on perseverative inhibitory or facilitatory tendencies, or upon frustration, fail to describe the data accurately. Instead, analysis of the data shows that the animals were accurately anticipating the quantity of reward to be obtained on each run, running fast for large quantities and slowly for small.

     

Coding of feature and no-feature events by pigeons performing a delayed conditional discrimination

Pigeons’ performance of a delayed conditional discrimination with presence versus absence of conditional (sample) stimuli was examined in two experiments. The pigeons showed steeper retention functions with feature (i.e., presence) samples (either food or yellow) than with no-feature (i.e., absence) samples (either no food or no yellow). These results suggest that pigeons code features and respond only by default to test stimuli (comparisons) associated with no features. In contrast, the overall superiority of performance on no-feature-sample trials compared with feature-sample trials in both the food/no-food- and yellow/no-yellow-sample tasks was reversed at a 0-sec delay in the food/no-food-sample group, but not in the yellow/non-yellow-sample group. This difference in results with hedonic versus nonhedonic samples suggests that the crossover in delay performance on food/no-food-sample trials is produced by the formation of backward associations between the food-associated comparison stimulus and the food sample.     

Development of excitatory backward associations during the establishment of forward associations in a delayed conditional discrimination by pigeons

The development of excitatory backward associations in pigeons was demonstrated in three experiments involving conditional discriminations with differential outcomes. In Phase 1 of all three experiments, correct comparison choices following one sample were followed by food, whereas correct comparison choices following the other sample were followed by presentation of an empty feeder. In Phase 2, the food and no-food events that served as outcomes in Phase 1 replaced the samples. When the associations tested in Phase 2 were consistent with the comparison-outcome associations developed in Phase 1, transfer performance was significantly better than when the Phase 2 associations were inconsistent with the Phase 1 associations. In Experiment 1, an identity matching-to-sample task was used with red and green samples and red and green comparisons. In Experiment 2, a symbolic matching task was used with shape samples and hue comparisons, and it was shown that the backward associations formed were between the trial outcome (food or no food) and the correct comparison. In Experiment 3, it was determined that the transfer effects observed in these experiments did not depend on either the similarity of behavior directed toward the samples in the training and test phases, or the similarity of food and no-foodexpectancies generated by the samples in Phase 1 to food and no-foodevents presented as samples in Phase 2.     

The feature-positive effect and sign-tracking behavior during discrimination learning in the rat

Feature-positive (FP) and feature-negative (FN) successive discrimination learning was investigated in the rat. When a discrete, visual element serving to differentiate the discriminanda belonged to S+ (FP), rats acquired the discrimination more rapidly than when it formed a part of S? (FN). During the course of training, FP rats developed a tendency to direct their responding toward the differentiating feature in S+ while FN rats shifted their responding away from this element in S?. These findings were discussed in terms of the conceptions of stimulus-reinforcer relations and “sign-tracking” behavior.     

Animal memory: The contribution of generalization decrement to delayed conditional discrimination retention functions

Delayed conditional discriminations in which a sample indicates which comparison stimulus is correct have typically been used in working memory research with animals. Following acquisition with no (0-sec) delay between the offset of the sample and the onset of the comparison stimuli, delays of variable duration are introduced. The resulting retention functions are taken as a measure of memory. We suggest that, in addition to memory loss due to the delay, the comparison of matching accuracy at the 0-sec training delay with relatively novel test delays may produce a generalization decrement that varies as a function of increasing delay. We tested this hypothesis by training pigeons with a mixed delay procedure from the start and found that the retention functions for these pigeons were significantly shallower than those for a control group trained with 0-sec delays and tested with longer delays, and, although reduced in magnitude, the differences persisted for as many as 15 sessions. We propose that a measure of animals’ working memory can be obtained uninfluenced by a generalization decrement if they have received comparable training with all of the delays that are tested.     

南音唱腔社会审美的时代性差异

南音千百年不断变化发展的流传与传承反映了不同时代、社会历史文化背景下人们审美价值取向、审美观的变化与发展.清末民初至今南音唱腔从以男性唱腔为主到以女性唱腔的转变、现今革新性唱腔与传统性唱腔的并存反映了不同历史条件下社会审美的时代性差异.     

Fading procedure effects on a visual pattern discrimination reversal in the albino rat

Two groups of albino rats were trained on a simultaneous pattern discrimination task, one with a classical procedure in which the discriminanda remained invariant throughout training, and the other with a fading procedure in which the final task was approached through a series of graduated steps. In a subsequent reversal stage, during which the initial positive stimulus became negative and vice versa, each group was subdivided so that half of the subjects in each original group received reversal training with the same procedure as during acquisition and the other half with the other method. Fading procedures yielded a more proficient performance on every occasion, independently of experimental stage or previous learning history. Results are analyzed in terms of favorable conditions offered by the procedure itself and of beneficial influences exerted over subsequent learning.     

论《啼笑因缘》的多重趣味组合

趣味是文学作品吸引读者的内因之一。《啼笑因缘》综合了情节、认知、时事、审美等多重德味，并在对情节趣味有所偏重的前提下，对各种趣味加以抑制与淡化处理，从而形成一种葱绿配桃红似的参差对照之美。     

The effect of discrimination training on the response rate and response duration of the rat

Response rate (responses per minute) and response duration (time in seconds per press) were recorded in rats shifted from multiple variable-interval variable-interval (mult VI VI) to multiple extinction variable-interval (mult EXT VI). This procedure produced positive contrast (i.e., a decrease in response rate in EXT and an increase in VI) in 11 of 12 rats and, in addition, produced an increase in response duration (i.e., bar holding), which, for the most part, was confined to the EXT component of the mult EXT VI condition. One of the 12 rats showed negative induction (i.e., a decrease in response rate in both the EXT and VI components), and also an increase in response duration in both the EXT and VI components of the mult EXT VI condition. The results indicate that generalization of behavior from the EXT to the VI component can produce negative induction, and that such generalization must be prevented if positive contrast is to occur in the rat.     

The importance of sensory context in young children's acceptance of salty tastes

Acceptance of and expressed preference for varying levels of salt (NaCl) were assessed among children 3-6 years of age. 20 children received 0, 0.17, and 0.34 M NaCl in aqueous solution, and 20 received these same NaCl concentrations in a soup broth. In both groups, children were asked to ingest as much as they wanted to each stimulus during brief, sequential presentations and to indicate which stimulus they preferred in a series of paired-comparison presentations. A striking, context-specific reaction to the taste of salt was observed on both measures. Children in this age group strongly rejected even the moderate level of salt in water relative to unsalted water. In contrast, the most highly salted soup was well accepted and preferred to either unsalted or moderately salted soup by the majority of children.     

Conditional discrimination in the goldfish

Two goldfish were reinforced for responding in the presence of a compound S+ consisting of a bright light and a loud sound. S? compounds differed from the S+ with respect to light intensity, sound intensity, or both. Responding in the presence of each compound was evaluated according to several alternative models of stimulus combination. The results permit rejection of some hypotheses concerning integrative processing in the goldfish.