Geometry learning while navigating: The importance of task difficulty and sex differences.

Abstract

Cheng (1986) trained male rats to search for food in a rectangular arena that also contained distinctive visual patterns. He found that the rats used mainly the geometric framework of the box itself to find the food and claimed that geometrical information is processed in a specialized module, which is independent of feature information. The aim of the present set of experiments was to check if the previous results with male rats and an appetitive task could be extended to an aversive task while using both male and female rats and three-dimensional landmarks. In Experiments 1 and 2, rats were trained in a rectangular-shaped pool to find a hidden platform that had a location defined in terms of two sources of information—landmarks of different salience (less salient in Experiment 1, more salient in Experiment 2) outside the pool and a particular corner of the pool. The results showed that both males and females used mainly the particular corner of the pool, supporting Cheng’s suggestion. In addition, in the two experiments, what the rats learned with respect to the landmarks was negligible. Experiment 3 used a more difficult triangular pool in addition to the rectangular pool, in the absence of landmarks. The results revealed sex differences in the triangular pool but not in the easier rectangular pool. These results suggest that task difficulty is a factor when it comes to finding sex differences in rats in spatial tasks.

Previous Experience Seems Crucial to Eliminate the Sex Gap in Geometry Learning When Solving a Navigation Task in Rats (Rattus norvegicus)

“…The results of Experiment 2A revealed that males and females did not differ in the initial learning speed to find the hidden platform in the Morris pool, neither during the pre-training escape trials, in the circular pool in the absence of the landmark, nor in the subsequent training phases with the hidden platform located in a certain corner of the kite-shaped pool (Training 1), of the rectangular-shaped pool (Training 2), and of the triangular-shaped pool–in the last case close to the landmark (Training 3). This suggests that females do not spend more time exploring the pool than males, but that both males and females seem to swim directly to the platform (see Forcano et al, 2009 and Chamizo et al, 2020 for similar results). The most relevant result of Experiment 2A is the shape test trial, without the platform (i.e., in the triangular pool and no landmark).…”

“…However, a recent set of experiments by Chamizo et al (2020) , using male and female rats and several modified Morris pools (as in the wet condition of Golob and Taube’s, 2002 ), has shown that both male and female rats primarily encode geometric information even when trained in the presence of salient visual cues, thus supporting Cheng’s initial results ( Cheng, 1986 ; see also Gallistel, 1990 ). In Experiments 1 and 2 of the study by Chamizo et al (2020) , male and female rats were trained in a modified pool (i.e., with a rectangular shape) to find a hidden platform, which was located based on two cues or sources of information, both next to the platform: one specific landmark (a target landmark), outside the pool, and one particular corner of the pool (a target corner). In both experiments the results revealed that geometry learning had clearly interfered with learning about the target landmark.…”

“…These findings were expected in male rats ( Rodríguez et al, 2010 , 2011b ; Keeley et al, 2013 ) but totally unexpected in females. Then in Experiment 3 ( Chamizo et al, 2020 ) the authors addressed the concept of task difficulty. The following speculation was carried out.…”

“…If learning in the rectangular-shaped pool was easier than learning in the triangular-shaped pool used by Rodríguez et al (2010 , Experiment 2; see also Chamizo et al, 2016 ; Rodríguez et al, 2011b ; Keeley et al, 2013 ), in part because the swimming surface was half the size in the rectangular pool than in the triangular pool, the results of Experiments 1 and 2 could be explained by appealing to the proposal of Coluccia and Louse (2004) that emphasises that sex differences tend to appear only when the task to be learned is difficult (see Forcano et al, 2009 , for a demonstration in a Morris pool). Experiment 3 ( Chamizo et al, 2020 ) was carried out in order to see if there would be differences in the speed with which the male and female rats learned a spatial task, a simple one, that was based solely on geometry. The experiment consisted of two groups of male rats and two groups of female rats and two shaped-pools (a rectangular shape and a triangular shape–as in Rodríguez et al, 2010 ) were used.…”

“…But many questions are still unanswered, waiting for further research. For example, could the previous sex differences in the triangular pool ( Keeley et al, 2013 ; Rodríguez et al, 2010 ; Chamizo et al, 2016 , 2020 ) disappear with prior experience with geometry? The main aim of the present work is to answer this question.…”