[This is page 6 of paper handout]
Results of exposure to a stimulus
(as in Walker 1987 p. 37 ff)
i) Sensory adaptation or fatigue
But Dethier (1963) showed that blowfly adaptation to certain sugar solution transferred from left to right leg — therefore more central. In fact generalized sensory adaptation could be marginal form of habituation. [Scheiner, 2004, tested habituation with different strengths of sugar solution applied to the antennae of honey bees.]
ii. Response fatigue
Response decline would be less interesting if due just to muscular exhaustion. But dishabituation with a second stimulus shows that it is not just a response-production process
iii. Habituation in the S-R connection:
“Habituation involves homosynaptic depression of the [presynaptic] terminal due to repeated activity of the sensory neurons” (Castellucci and Kandel, 1976). There are decrements in excitatory post-synaptic potentials of the motor cell, because pre-synaptic terminals of sensory cell release less transmitter substance. Thus it is the central synapses between sensory input and motor output that habituate.
iv. Sensitization and Sensitized states
Often there is opposite of habituation like “warm-up”: Sensitization means that the early stages of repeated exposure to a stimulus are characterised by increases in the strength of the responses made to the stimulus. Groves and Thompson have separated habituating synapses and sensitized circuits, even in spinal cords. (Groves & Thompson 1970: see overhead on sheet 8). Kandel’s Nobel lecture included a section on results obtained using sensitization as a test of memory processes (Kandel, 2001: this was sensitization induced by using a strong stimulus to sensitize reponses to a weaker stimlus.).
v. Familiarity by memory formation of the stimulus.
Sometimes called “extinction of the orienting reflex” which is confusing, but refers to changes in attention peripherally very observable in infants. Alternatively “Formation of a neuronal model of the stimulus”
vi.. Decreased attention to familiar stimuli (Sokolov, sheet 7)
Attention can be indicated by desynchronisation of EEG and eye turning. Plus dilation of blood vessels in the head and drop in resistance of skin of hands (“GSR”).Thus gating of incoming stimuli, which must involve multi-stage hierarchically organized perceptual systems. This cannot happen in the same way with spinal or ganglionic reflexes. even though some ecological functions are similar.
vii. Increased capacities for discrimination and classification.
By exposure, increased perceptual accuracy (Hebb, 1949) .Gibson and Walk (1956): rats reared in cages with bas-reliefs of circles and triangles on the walls were better at experimental discrimination. Thus “Perceptual learning” exposure learning or “latent learning”. The main function of perception is not to become indifferent but to acquire useful information. The ecological function of habituation is more widespread with complex perceptual systems. In more complex systems the ecological function is stimulus recognition. (Imprinting is an example of this.)