Lack of generalization of object discrimination between spatial contexts by a bat

Abstract

SUMMARY Discrimination and generalization are important elements of cognition in the daily lives of animals. Nectar-feeding bats detect flowers by olfaction and probably vision, but also use echolocation and echo-perception of flowers in immediate target surroundings. The echo received from an interference-rich flower corolla is a function of a bat's own relative position in space. This raises the question how easily a free-flying bat will generalize an echo stimulus from a learning situation to a new spatial context where differences in relative flight approach trajectories may lead to an unfamiliar spectral composition of the self-generated echoes. We trained free-flying Glossophaga soricina in echoacoustic discrimination in a two-alternative forced-choice (2-AFC) paradigm at location A. We then tested at location B for spontaneous transfer of discrimination ability. Bats did not spontaneously transfer the discrimination ability acquired at A to location B. This lack of spontaneous generalization may have been caused by factors of the underlying learning mechanisms. 2-AFC tasks may not be representative of the natural foraging behaviour of flower-visiting bats. In contrast to insect-eating bats that constantly evaluate the environment to detect unpredictable prey, the spatial stability of flowers may allow flower visitors to rely on spatial memory to guide foraging. The 2-AFC task requires the disregard (learned irrelevance) of salient spatial location cues that are different at each new location. In Glossophaga, a conjunction between spatial context and 2-AFC discrimination learning may have inhibited the transfer of learned irrelevance of spatial location in the 2-AFC task to new spatial locations. Alternatively, the bats may have learnt the second discrimination task completely anew, and were faster only because of an acquired learning set. We suggest a dissociation between 2-AFC task acquisition and novel object discrimination learning to resolve the issue.

Niche-specific cognitive strategies: object memory interferes with spatial memory in the predatory bat, Myotis nattereri

“…We suggest that, given the choice, predatory bats are more likely to rely on object memory than spatial memory for finding profitable prey and avoiding unprofitable prey. Taken together with results from frugivorous and nectivorous species, our results support Stich and Winter's (Stich and Winter, 2006) niche-specific cognitive strategies hypothesis in bats. This hypothesis falls under the umbrella of the more general hypothesis of a cognitive continuum comprising closely related vertebrate species that differ in foraging behaviour and diet [e.g.…”

“…Jensen et al, 2005;Mueller and Mueller, 1979;Schnitzler et al, 2003;Surlykke et al, 2009). In the present study, we concur with Stich and Winter's (Stich and Winter, 2006) dietspecific predictions and extend this hypothesis to bats other than phyllostomids.…”

“…Consistent with this hypothesis, in the nectivorous and frugivorous phyllostomid bats Glossophaga soricina and Carollia perspicillata, spatial memory during foraging takes precedence over other sources of sensory information (e.g. flower shape, olfaction, colour) once the bats have identified potential food resources (Carter et al, 2010;Thiele and Winter, 2005;Stich and Winter, 2006). For fruit-and nectar-feeding bats, relying on spatial memory to relocate stationary, nutritional resources such as ripe fruit and recently produced nectar should be advantageous.…”

“…In G. soricina and C. perspicilatta, spatial memory profoundly overshadows object memory learning (Carter et al, 2010;Stich and Winter, 2006;Thiele and Winter, 2005). Experiments with predatory bat species often randomize reward position to overcome the potential impact of spatial memory on cue-consequence associative learning (e.g.…”

“…In some species, spatial memory is essential for migration (Griffin, 1970;Holland, 2007;Schnitzler et al, 2003;McGuire and Ratcliffe, 2011;Tsoar et al, 2011). Stich and Winter (Stich and Winter, 2006) proposed the nichespecific cognitive strategies hypothesis for phyllostomid bats, predicting that nectar-feeding and fruit-eating species should rely more on spatial memory, while predatory species should rely more on object memory. Consistent with this hypothesis, in the nectivorous and frugivorous phyllostomid bats Glossophaga soricina and Carollia perspicillata, spatial memory during foraging takes precedence over other sources of sensory information (e.g.…”