Key Questions for today:
- How do animals learn to react differently in the presence of different stimuli?
(simple discrimination)
- How are those processes modified when we are dealing with categories of stimuli
rather than the same stimuli over and over again? (complex discrimination)
Contents today:
- We will use the principles already studied to attempt to account for more complex
behaviours
- The general idea is that we build up complex behaviour from simple conditioning
based on more sophisticated representations
- Always keep in mind Lloyd Morgan’s canon – keeping things as simple as we can
Early conditioning studies used simple Discrimination
From Pavlov onwards, learning theorists experimented with providing the unconditioned
stimulus (classical conditioning) or reinforcement (in operant conditioning) in the presence
of one stimulus (sometimes called the CS+ or S+) but not in the presence of another
(sometimes called CS- or S-)
- In general, different responding can be obtained to each stimulus, and we say that
the animal can discriminate between the 2 stimuli
- In early experiments, the stimuli were normally simple, and they different on some
obvious physical dimension (e.g: tones of a different pitch, lights of a different colur)
Procedures and apparatus involved in simple discrimination studies
Procedures:
- Successive discimintation: present one of the stimuli and see how the animal
responds
- Simultaneous discrimination: present 2 stimuli and see which the animal chooses
- Conditional discrimination: reinforce different responses (or different stimulus-
response associations) in the presence of different stimuli
Apparatus:
- Discrimination boxes (mazes with discriminative stimuli added)
- Lashley’s jumping stand
- Harlow’s Wisconsin General Test Apparatus (WGTA)
- Skinner boxes (many variations of this)
- Nowadays video and computer displays are used as well as touch screens
, Successive and Simultaneous Discriminations
Successive Discrimination
- The animal is shown one stimulus and typically has to decide whether to respond or
not.
- In some cases, the stimulus that the animal is supposed to respond to is S+ and the
other one that it is not meant to respond to is D-.
- If it mistakenly responds to S-, there will be no reward
Simultaneous Discrimination
- Typically 2 stimuli are presented on a trial and the anial has to choose one
- It makes its choice by choosing 1 of 2 keys or by pecking the stimulus
- If it chooses the right one it gets a reward whereas the wrong one (S-) produces no
reward and a time out
- The stimuli swap sides at random to avoid the animal responding on the basis of
position
Complex Discriminations
Following a pioneering experiment of Hernsetin & Loveland (1964) much modern work as
concentrated on experiments on discrimination between sets of stimuli
- The stimulus sets are usually defined in terms of human concepts (e.g: person vs
non-person, fish vs non-fish) or artificial concepts defined by specified multiple
features.
Such categorical discriminations are frequently learned quite quickly. Most discussion has
centred on the question of whether animals need to possess concepts in order to perform
categorical discriminations- and what it would mean for an animal to possess a concept.
Two kinds of abstraction
The idea of complex discrimination is based on the fact that classification and responding on
the basis of stimulus similarity is what we call categorisation – and can be performed using
the same types of learning algorithm (like Rescorla-Wagner) that we’ve considered so fa
Perceptual categories: observable categories such as cats. These can be perceived and the
only abstraction is that the cats look slightly
different, but they are all clearly cats
Logical categories: Categories that are more abstract and require logic such as number
groups. If you had just groups of 4, the objects that are grouped into 4’s may not all be the
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