Visual discrimination learning tasks

Winneke et al (1982b) carried out an interesting study which demonstrates how relevant the nature of the learning task is. In their study rats were dosed pre- and post-natally with lead. Animals were tested on a two-way active avoidance task, and later on a visual discrimination task. In the discrimination task the performance of lead-dosed animals was inferior to the controls. In the avoidance task the performance of animals improved significantly in a dose-related fashion, with increasing lead level. 

The results are inconsistent with those of the previous study, to the extent that there was no significant difference in the visual discrimination learning between the groups. In the spatial learning task there were significant differences in the number of days required to reach criterion, with the performance of both maternally and permanently exposed groups inferior to that of controls. 

In contrast to previous observations there were no group differences for errors in the acquisition phase of visual discrimination learning at the age of 100 days. After 6 weeks retention of the task was significantly impaired (p < 0.01 Figure 1) in all lead-exposed groups as compared to controls. There were no differences between maternally and permanently exposed animals... 

Abstract For most mammals, the ability to detect odours and discriminate between them is necessary for survival. Information regarding the availability of food, the presence of predators and the sex, age and dominance status of conspecifics is odour mediated. Probably because of this extraordinary reliance upon odour cues, mice and rats have developed the ability to learn and remember information associated with olfactory cues as effectively as primates recall visually related cues. As a result, these rodents have become the model of choice to study the neural and cognitive processes involved in olfactory discrimination. In this paper, we describe some of the more ethologically based tasks used in assessing olfactory discrimination and the advantages and disadvantages of the different methodologies employed. 

On a task of visual discrimination - the Karni-Sagi task, for example - individuals improve their performance without knowing how or why (as they learn the task) after sleep they then do better... 

Myhrer, T. (2000). Effects of selective perirhinal and postrhinal lesions on acquisition and retention of a visual discrimination task in rats. Neurobiol. Learn. Mem. 73 68-78. 

One way to test these ideas is to examine humans or animals who from birth had no visual experience, and thus no opportunities for visual learning, and to test them when their sight is restored. Perceptual functions are then tested to see which, if any, are intact. This was done with human beings bom blind because of cataracts before surgical methods were developed to safely remove them. Cataracts are a disease of the eye in which the crystalline lens or its capsule are or become opaque. It was found that after their cataracts were removed they were normally responsive to changes in color and light, but they were unable to tell when a figure was present, or to discriminate between simple shapes. It took a period of two to three months before they were able to perform these tasks with ease. 

In the raty dizocilpine (75 Jig/kg) had no effect on the acquisition of a spatial discrimination task in a Y-maze, but disrupted reversal learning (Cross et al. 1995). Both the acquisition and reversal of a visual discrimination task were impaired following dizocilpine (75 ig/kg). Dizocilpine (40 ig/kg) also disrupted performance of a five-choice visual reaction time task. 

When retested the performance of both lead-dosed groups was inferior to that of controls, on both the tests. The performance of the maternally dosed animals resembled that of the permanently dosed animals despite the fact that their blood and brain levels were comparable to those of the controls. This implies that early damage is irreversible, and that further exposure does not exacerbate this effect. The study also highlights the functional difference between learning and memory, as there was no difference in the learning of the visual discrimination task, but there were differences in the retention of this skill. 

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