Discrimination learning

Ten male albino rats were trained In a brightness discrimination
problem where they were reQuired to choose a sttmulus value of
0.053 ft/cd over one of 0.012 ft/cd. Pairs were matched accordlng to
the number of trials requtred to reach a criterion of 18/20 correct
responses then randomly assigned to one of two grouos for testing In
transposition. Both groups were tested on the orlgtnally positive stimulus and a brighter one: 1.25 ft/cd for Group 8-C and 5.38 ft/cd
for Group 8-D. By testing for transposttlon wtth non-reinforced trials, contrary to the usual method, a tendency toward converging measures
of transposltton was achteved. Transposition for Group 8-D, In the
situation most dissimilar to training, was greater than for 8-C.
These results were discussed from relational or Gestalt, Spence model,
and Adaptation Level positions and It was shown that the results are
contrary to traditional Gestalt predictions. It was oredlcted that, according to underlying assumptions of
the Spence model, with continued non-reinforced trials, per cent of
transposition for both groups would decrease until a chance level of
responding was reached. That this did not occur cannot be explained
by the Spence model. Because the variability was too great with such a small N,
these results did not reach the .05 level of probability.

Twenty 100 day old male rats were trained to behavioral criterion in a CER paradigm. Two shock levels (.1 and .2 ma) were employed to establish these criteria. Half of the Ss reached medium suppression (suppression ratios between .39 and .11) of a bar pressing response; half achieved high suppression (suppression ratios less than .10). The animals were subsequently exposed to 15 daily sessions of FI training utilizing a head, panel pressing response for food. Five of the medium suppression group and five of the high suppression group were exposed to the conditioned suppression CS (a light) during the FI acquisition periods . The remaining rats underwent FI training in the absence of the CS. An Index of Curvature was employed to measure each FI period record and to indicate the degree of acquisition of FI scalloping. Analysis of variance for the four groups revealed only the progression over days to be a significant source of variation. Analysis of linear trend indicated a strong linearity in the variance over 15 days for all groups, but revealed no clear differences between the groups. Some tendencies indicate a slight superiority in acquisition by the medium suppression group which was exposed to the CS during FI training. The high suppression group which was exposed to the light was noticeably inferior in FI discrimination. These results possibly demonstrate an "arousal- interference" mechanism for the CER, but the data do not support the conclusion that the conditioned suppression signal (CS) has a differential effect on subsequent acquisition of an unrelated temporal discrimination. A history of shook treatment, or of CER training, may be responsible, however, for the overall poor acquisition of FI scalloping that was demonstrated by all four groups in this study.

The effect of stimulus plane orientation (horizontal vs
vertical) on mirror-image oblique discrimination was
investigated for children 5 to 8 years of age. A
significant difference in learning rate favoring the
vertical plane presentation was obtained. Tracing the
stimuli had no effect on learning rate in either the
horizontal or vertical plane. The results were explained
in terms of egocentricity in the child's representation of
spatial relations.

An attempt was made to investigate the intradimensional
transfer of a simultaneously presented, double brightness discrimination
in male hooded rats. It was hypothesized that in
a paradigm designed to emphasize interstimulus cues over
individual stimulus cues, subjects would exhibit transposition
in testing, even when this involved approaching a previously
negative stimulus, and avoiding a previously positive stimulus,
under extinction conditions. Results of two tests (with a partial reinforcement retraining
session between them) indicated significant transposition
on all measures except trial of first choice on Test I
for the group trained to approach the brighter stimulus in any
pair presented. Results were interpreted as being in support
of relational theory which stresses the importance of dimensional
salience in the establishment of relational responding.

Twenty-four rats were trained to avoid shock in a shuttlebox,
receiving feedback for a correct response. During extinction,
matched pairs were tested under response contingent or
response independent feedback, with either shock or no shock. The combination of response contingent feedback and no shock
led to the greatest resistance to extinction. No other significant
differences were found. The results were used to support
the discrimination hypothesis, and concurred with other studies
with regard to: (1) the functional similarity of feedback and
CS termination in the acquisition and maintenance of avoidance,
and (2) the importance of the interaction of the response contingency
with the avoidance contingency, in determining the
effects on avoidance responding.

An attempt was made to investigate the abstract concept
of relation. It was hypothesized that the learning of the
relational concept independent of particular stimuli or
dimensions is possible even in nonverbal animals. One group
of rats was trained on a discrimination that could only be
solved with relational learning; a second group of rats was
trained on a discrimination that could be solved only with
absolute learning. Both groups were then trained on a
discrimination that could be learned in either a relational
or absolute manner, and transposition testing was done to
determine the method utilized. Results indicated animals with original relational
learning solved the second discrimination relationally;
animal s with original specific learning solved the second
discrimination in an absolute manner.

An attempt was made to determine the effects of
successive shifts in the quality of a reinforcing agent
upon the acquisition of a brightness discrimination. Two
levels of sucrose concentration (4 and 32%) were combined
factorially during preadaptation and discrimination phases.
Dependent measures included response rate and the number
of errors made during discrimination acquisition. Results indicated non-significant negative contrast
effects in errors and, in addition, negative contrast and
amount of reward effects in terms of response rate. It was
hypothesized that the absence of amount of reward effects
in errors and positive contrast in both dependent measures
was a function of a partial between groups design and
ceiling effects respectively.

Eighteen rats were used to study two procedures for the
extinction of discriminated avoidance. One group (OE) was
placed on extinction defined by presenting shocks as programmed
but independently of the S's responses, while the other group
(CE) was placed on classical extinction defined by the removal
of all shocks. The two procedures were compared in terms of
rate of decline and terminal level of extinction performance.
In addition, the two groups were placed on a discrimination
reversal task in order to assess each procedure's effects on
a new learning problem. The CE group reached a lower level of
extinction performance in a fewer number of blocks than the
OE Ss. Furthermore, the CE Ss were inferior to the OE Ss in
terms of discrimination reversal performance as well.
An interpretation of the results in terms of the removal
and reinstatement of cues was offered although an alternative
explanation relating to a change in the motivational states
of the two groups during extinction was also presented. The
interpretation in terms of the presence or absence of cues
seemed to account for more of the present findings than the
traditional one advocating changes in motivational levels
resulting from the two divergent extinction operations.

The Big Cypress Swamp and the Everglades of South Florida are inherently oligotrophic ecosystems that in recent decades have been subjected to increasing agricultural nutrient inputs. While extensive research regarding deleterious effects of nutrient impacts has been conducted in the phosphorus-deficient Everglades, there is a lack of research in Big Cypress Swamp. This 12-month field study assessed the responsiveness of Taxodium distichum, Fraxinus caroliniana, and herbaceous vegetation to increased nutrient levels in Big Cypress Swamp. Six nutrient treatments (Control, N, P, K, 2K, and PxK) were applied to the soil surrounding these trees. F. caroliniana had higher photosynthetic rates with 2K treatments and higher growth rates with PxK treatments. T. distichum had higher Leaf Area Index in the P and PxK treatment but did not exhibit other responses to treatment. Herbaceous vegetation showed little response to treatments. This study concluded that potassium may be co-limiting in this ecosystem.