Non-Associative Learning - Behavior

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Non-Associative Learning

  • Non-Associative Learning: is learning that does not require linking or associating stimuli together. It is considered the simplest type of learning and therefore a topic which can help us gain fundamental insight into learning.
  • We will discuss three types of non-associative learning:
    • Habituation: A decrease in behavior due to repeated exposure to an innocuous stimuli
    • Sensitization: An increase in behavior due to exposure to a noxious stimulus
    • Perceptual Learning: Learning to process stimuli more rapidly and to distinguish similar stimuli from each other

Habituation

  • Habituation is a decrease in behavior due to repeated exposure to an innocuous stimulus
  • Spontaneous Recovery: When stimulation ends, behavior recovers (forgetting!).
  • Specificity: Habituation is relatively specific the the stimulus presented; a different stimulus will not produce a habituated response
  • Dishabituation: Exposure to a new often disrupts, removes habituation to a prior stimulus, especially if the new stimulus is somewhat noxious
  • Habituation is ubiquitous--it occurs in all known animals

Some behaviors that habituate include

  • Acoustic startle reflex: play a loud noise an measure how intensely the participant jumps. With repeated loud noises, the participant jumps less and less. Usually done with rats.
  • Orienting response: show a new visual stimulus, and the participant will turn to look at it. With repeated presentations, the participant will look at the stimulus for less and less time. Usually done with humans, especially infants.
  • Gill-Withdrawal Reflex: In Aplysia, stimulating the siphon produces a withdrawal of the gill and siphon. With repeated stimulation, the animal will withdrawal for less and less time.

Factors that influence habituation

  • Repetition: More stimulation, more habituation
  • Inter-stimulus interval (ISI): With more rapid stimulation, habituation is more rapid, and deeper, but it doesn't last as long.
  • Stimulus Intensity: The stronger the stimulation, the less habituation occurs
  • Spacing: Spaced training (separation between training) produces weaker, but longer-lasting habituation


Sensitization

  • Sensitization is an increase in behavior due to exposure to a noxious (painful) stimulus
  • Sensitization is different from habituation:
    • Occurs due to strong/painful stimulation (habituation occurs due to weak stimulation)
    • Can occur with a single painful stimulation (habituation requires repeated stimulation)
    • Increases behavior (habituation decreases behavior)

Factors that influence sensitization

  • Repetition: More noxious stimulation, more sensitization
  • Stimulus Intensity: Stronger stimulus, more sensitization
  • Spacing: Spaced training (separation betweeen training) produces longer-lasting sensitization


Perceptual Learning

  • Perceptual learning is the ability to learn to recognize a stimulus more quickly and/or to tell the difference between two similar stimuli
  • Priming is an example of perceptual learning: seeing a stimulus before makes you faster at recognizing it later.
  • Discrimination Training' is a way of teaching perceptual learning. An animal is shown different but similar stimuli and trained to only respond to one specific type of stimulus.
  • Mere exposure: Perceptual training does not seem to require conscious effort, but instead seems to occur from merely being exposed to new stimuli.


Models of Non-Associative Learning

Dual-Process Theory

  • Developed by Groves and Thompson
  • Suggests two pathways for each reflex
    • Low-threshold pathway that weakens with activation
    • High-threshold pathway that strengthens with activation
  • According to dual-process theory every stimulus produces at least some weakening and some strengthening of the response. Sensitization and habituation simply reflect extreme examples where a single process is mostly activated.
  • Dual-process theory may also account for some perceptual learning, as it may allow important components to a stimulus to increase strength and unimportant components to decrease
  • This model has a strong neural plausibility and has matched or predicted many features of habituation and sensitization.

Comparator Models

  • According to the comparator model, each time a stimulus occurs, it is compared to the stored memory of it.
  • If there is a difference between the memory and the real stimulus, the animal pays attention to the stimulus and stores more information
  • Thus, over repeated stimulation, the memory builds in quality and the animal pays less and less attention to it
  • This model has been criticized because it is difficult to objectively measure 'the quality of the memory' or what it means to store a memory


Mechanisms of Non-Associative Learning

Simple systems approach

  • Mammals have billions of neurons, making it too complex to get a good understanding of how the nervous system functions. Since many psychological phenomena are conserved across the animal kingdom, we may make better progress by studying the same processes in simpler organisms.
  • Eric KandelAplysia californica – a sea slug; 10,000 large neurons, ideal for understanding nervous system
  • Seymour BenzerDrosophila melanogaster – the frutifly; several million neurons and a short lifespan ideal for genetics
  • Sydney BrennerCaenorhabditis elegans – a nematode (roundworm); only 300 neurons and 1000 cells, simplest animal to study development

Aplysia siphon withdrawal reflex

Aplysia.jpg

  • Aplysia are large marine gastropod mollusks
  • The siphon is a straw-like structure that contracts to expel water from the gill
  • Siphon-withdrawal reflex (SWR) and Gill-Withdrawal Reflex (GWR) – touching the siphon causes it and the gill to withdrawal (SWR). Touching the gill causes it to withdraw (GWR). Either reflex can be measured as duration (in seconds) of the contraction or the threshold (in newtons) for responding

Non-Associative Learning in Aplysia

  • Repeated siphon stimulation produces a short-term habituation lasting a few hours. Repeating multiple training sessions produces a long-term habituation lasting days to weeks
  • Noxious shock to the tail causes an increase in the SWR and GWR. A single shock increases the reflex for 15 minutes to an hour. Repeated shocks can cause sensitization lasting days to weeks

Neural Mechanisms

  • SWR is controlled by a simple, three-layer neural circuit: sensoryneuron -> interneuron -> motor neuron
  • Short-term habituation
    • Kandel found that during habituation, sensory neurons release less neurotransmitter. This is due to a change in the calcium channel proteins that regulate neurotransmitter release. After some time, the channels are replaced with new ones, and the memory is lost.
  • Long-term habituation
    • Glanzman et al. found a requirement for protein synthesis. This means that new transcription factors had been activated, altering the patterns of genes expressed, and thus of protein made. This type of change is thought to be relatively permanent.
  • Short-term sensitization
    • Kandel found that tail shock causes the release of serotonin, which modulates sensory neurons to release more neurotransmitter at the next touch, causing stronger reflex reactions


Applications of Habituation

Probing sensory function and categorization

  • Generalization is a function of stimulus similarity. If a new stimulus completely generalizes, the subject basically can’t tell the difference between it and the training stimulus. If a new stimulus doesn’t generalize at all, the subject perceives the training and test stimuli quite differently.
  • Using this reasoning, researchers have used habituation to probe how infants perceive the world
  • Infants are given different stimuli while sucking on an electronic pacifier. New stimuli cause intense sucking, but with repeated presentation, sucking decreases. Eye gaze can also be used as a dependent variable.
  • For example, if habituated to a woman’s face, will an infant respond to a man’s face? How old does an infant have to be to tell the difference between men and woman?
  • Johnson and Aslin (1995) habituated infants to a line occluded by a box. They then tested for generalization to a straight line or to a line with a gap in it. Infants generalized to the straight line but not to the gapped line. This suggests that infants mentally ‘filled in’ the line through the occluding box.
  • This is not only theoretically interesting; there is interest in using these types of habituation tests as a early diagnostic for vision problems, enabling earlier correction

An early intelligence measure

  • Different infants habituate to the same stimuli at different rates
  • There is a correlation with the speed of habituation and later IQ scores. Faster habituaters have higher IQs. Interestingly, this correlation is orthogonal to social-economic status, gender, and race.
  • Again, this could become a practical way of screening early for developmental problems

A lie detector

  • With repeated viewing of an object, brain activity habituates
  • This could be a marker of ‘guilty knowledge’—when shown images only the criminal would have seen, the actual perpetrator should have less brain activity than innocent individuals
  • This potential usage is highly controversial, and studies have not yet shown a high level of reliability. However, there is intense interest in this research from law-enforcement, criminal justice advocates, etc. Could it become the DNA-test of the future?