Mapping the tip of the tongue--deprivation, sensory sensitisation, and oral haptics.

We investigated the impact of food deprivation on oral and manual haptic size perception of food and non-food objects. From relevant theories (need-proportional perception, motivated perception, frustrative nonreward, perceptual defence, and sensory sensitisation) at least four completely different competing predictions can be derived. Testing these predictions, we found across four experiments that participants estimated the length of both non-food and food objects to be larger when hungry than when satiated, which was true only for oral haptic perception, while manual haptic perception was not influenced by hunger state. Subjectively reported hunger correlated positively with estimated object size in oral, but not in manual, haptic perception. The impact of food deprivation on oral perception vanished after oral stimulations even for hungry individuals. These results favour a sensory sensitisation account maintaining that hunger itself does not alter oral perception but the accompanying lack of sensory stimulation of the oral mucosa. Both oral and manual haptic perception tended to underestimate actual object size. Finally, an enhancing effect of domain-target matching was found, ie food objects were perceived larger by oral than by manual haptics, while non-food objects were perceived larger by manual than by oral haptics.