Range and Absolute Odour Intensity Affect Olfactory Generalisation in the Honeybee
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Range and Absolute Odour Intensity Affect Olfactory Generalisation in the Honeybee Amir Fujita Choudhary
Revised: 4 December 2012 / Accepted: 10 December 2012 / Published online: 30 December 2012 # Springer Science+Business Media New York 2012
Abstract The human olfactory psychophysical literature is rich with anecdotal reports of variation in the perceived quality between weak and strong concentrations of the same odour (Wilson and Stevenson 2006). Psychophysical experiments using animals have also found similar effects of concentration on odour quality. The proboscis extension reflex (PER) is an appetitive Pavlovian conditioning assay that has been used to investigate olfactory stimuli in the honeybee. In this series of experiments I aim to identify the sensitivity of honeybees to changes in odorant concentration across the range of a honeybee’s sensorium (0.01–100 Pa). I compared generalisation to test odours that differed in molecular identity, odour concentration or both and found that large changes in odorant concentration (1,000 fold change) can produce greater shifts in perceptual similarity than a change in the odorant’s molecular structure. Our findings suggest a failure in concentration invariance when identical odours differ greatly in concentration. I also found poorer olfactory sensitivity (between identical odours of differing concentration) and acuity (between novel odours of identical concentration) at low odour concentrations (0.01 Pa). Keywords Olfaction . concentration invariance . odour intensity . Weber fraction . classical conditioning
Introduction The degree to which an animal responds to a novel stimulus following the formation of an association to another stimulus, the CS+ (conditioned stimulus), is termed generalisation. Responding to novel stimuli may initially seem like a mistake, however generalisation may actually represent an adaptive mechanism that allows an animal to learn associations between complex naturally occurring stimuli and the
A. F. Choudhary (*) Newcastle University, Newcastle, Tyne and Wear, UK e-mail: [email protected]
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J Insect Behav (2013) 26:577–591
rewards or dangers that they may predict. Floral odours can be composed of hundreds of different volatile compounds. The composition and concentration of these odorants may differ between flowers on the same plant depending on the time of year or even the time of day. A bee that restricts its foraging pattern to only a particular fragrance, may disregard profitable foraging sources, whist a bee that generalises too broadly may waste energy visiting flowers that contain little reward (Table 1). Studies of olfactory generalisation have been used to measure the perceptual similarity of odours and the molecular features that cause perceptual differences between them. Several studies, including those with honeybees (Guerrieri et al. 2005; Laska et al. 1999; Vareschi 1971), rodents (Cleland et al. 2002; Cleland and Narla 2003; Laska et al. 2006), primates and humans (Laska et al. 2000; Laska and Hubener 2001; La
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