Different parameters support generalization and discrimination learning in Drosophila at the flight simulator

Abstract

We have used a genetically tractable model system, the fruit fly Drosophila melanogaster to study the interdependence between sensory processing and associative processing on learning performance. We investigated the influence of variations in the physical and predictive properties of color stimuli in several different operant-conditioning procedures on the subsequent learning performance. These procedures included context and stimulus generalization as well as color, compound, and conditional discrimination (colors and patterns). A surprisingly complex dependence of the learning performance on the colors' physical and predictive properties emerged, which was clarified by taking into account the fly-subjective perception of the color stimuli. Based on estimates of the stimuli's color and brightness values, we propose that the different tasks are supported by different parameters of the color stimuli; generalization occurs only if the chromaticity is sufficiently similar, whereas discrimination learning relies on brightness differences.All animals extract relevant cues from the continuum of the incoming sensory stream to learn about their environment and how to behave in it. But how are the salient, predictive cues extracted from this stream and what factors determine the composition of a memory template? Obviously, some things are learned faster and remembered better than others. The relative timing of stimuli is of course paramount (for discussion, see Brembs

Context and occasion setting in Drosophila visual learning

“…Higher-order learning (occasion setting) appears to be independent of this function of the mushroom bodies. There is evidence suggesting that the reason for this independence lies in the different processing of generalization vs. discrimination tasks (Brembs and Hempel de Ibarra 2006).…”

“…Traditionally, researchers distinguished between predictive stimuli and mere "context" either by the physical properties of the stimuli (e.g., Bouton et al 1999), or according to their temporal relationship to the US (e.g., Wickens 1987). The work on Drosophila at the flight simulator demonstrated that both physical properties (Liu et al 1999;Brembs and Hempel de Ibarra 2006) and the nature of the predictive relation to the reinforcer (this study) are critical for the decision of whether to treat two situations as equivalent or as fundamentally different. The fewer the changes between situations, the more pronounced the impact of the physical properties of the situation (Liu et al 1999;Brembs and Hempel de Ibarra 2006); the more changes, the more pronounced the role of the changes and their relationship to the reinforcement (this work; see also Swartzentruber 1991;Myers and Gluck 1994).…”

“…The work on Drosophila at the flight simulator demonstrated that both physical properties (Liu et al 1999;Brembs and Hempel de Ibarra 2006) and the nature of the predictive relation to the reinforcer (this study) are critical for the decision of whether to treat two situations as equivalent or as fundamentally different. The fewer the changes between situations, the more pronounced the impact of the physical properties of the situation (Liu et al 1999;Brembs and Hempel de Ibarra 2006); the more changes, the more pronounced the role of the changes and their relationship to the reinforcement (this work; see also Swartzentruber 1991;Myers and Gluck 1994). Thus, for the general organization of learning experiments, it must be emphasized that the classification of stimuli as "context" is less obvious and self-explanatory than it might seem.…”

“…The conundrum is not enlightened by a large number of terms denoting the same or very similar experimental situations. Context generalization (this study; Liu et al 1999;Brembs and Hempel de Ibarra 2006) takes place when a memory can be transferred between different contexts (context-independent memory). Contextual learning or context conditioning (e.g., Colwill et al 1988b;Kim and Fanselow 1992;Debiec et al 2002) refers to experiments in which different contexts predict the occurrence or nonoccurrence of otherwise unsignaled USs.…”

Spontaneous decisions and operant conditioning in fruit flies

“…green or blue) or the temperature (i.e., infrared) of its environment. Various combinations of all these possibilities have been realized and are too numerous to mention here Heisenberg, 1986, 1997;Ernst, 1999;Heisenberg et al, 2001;Brembs and Heisenberg, 2001;Tang et al, 2004;Liu et al, 2006;Brembs and Hempel De Ibarra, 2006;Brembs and Wiener, 2006). Important for the argument made here is the possibility to allow the spontaneous decisions to turn in one direc- tion, say, right turning (positive torque values in Fig.…”