Sensitive Periods• During development there

are specific times when a biological event is more ‘sensitive’ to environmental stimuli e.g. language acquisition (age 3-7) – i.e. a SENSITIVE PERIOD

• We can still learn after the sensitive period has closed, but the learning process is less efficient.

• Note: Sensitive periods start and end gradually

Critical Periods• Refers to a finite period in which an

organism has heightened sensitivity to external stimuli that are compulsory for development of a particular skill

• e.g. certain areas of the visual cortex are only capable of synapse formation during early stages of development, once the crucial period has elapsed the individual will have some visual impairment

• E.g. Hubel & Wiesal temporarily blindfolded a kitten during a critical period (of visual development) from birth to 3 months when the blindfold was taken off, it never fully developed vision in the blindfolded eye. It actually resulted in reduced dendritic branching at the end of the neuron in comparison to the non deprived eye which had increased afferent activity as the eye developed.

Sensitive period vs Critical periods

Sensitive periods Critical periods

Starts and ends Gradually abruptly

During the period It is a period of maximal sensitivity

The organism has heightened sensitivity to external stimuli that are

compulsory for development of a

particular skillAfter the period The skill can still be learned,

but less efficientlyThe cortical areas

allocated for the particular skill will adapt and perform a different

function.Examples Language development Full development of visual

capabilities (from @ 8 months to 3 years)

Experience expectant learning• During EXPERIENCE EXPECTANT

LEARNING – the brain ‘expects’ and is primed for being exposed to the environmental ‘experience’ resulting in a rewiring of the brain (i.e. the establishment of a neural pathway resulting in learning)

• E.g the brain expects to be exposed to visual images, sounds, etc. in order for our visual, auditory, etc systems to develop.

Experience dependent learning• EXPERIENCE DEPENDENT

LEARNING – refers to additional skills developed over the lifespan (that the brain doesn’t expect

• E.g. an eskimo child learning how to build an igloo – which may be dependent on Observational learning (or Operant conditioning)

• There is no optimal period for experience dependent learning e.g. you can learn how drive when your 16, 30 or 50 (older people may struggle due to age related memory decline e.g. slowing of the Central.N.S)

Experience Expectant vs Experience Dependent Learning

Experience expectant learning Experience dependent learning

Stage of Lifespan that the genetic structural modifications occur

Early in life Over the lifespan in response to complex environmental

stimuli

During which period During the ‘Sensitive Periods’ There is no optimal period i.e. It occurs over the lifespan

Language Development of primary language (the brain expects to be exposed to

language)

Development of 2nd Language (it is dependent on exposure

to environmental stimuli)General or Specific General – e.g. We are all exposed

to visual stimuli, thus the brain expects and is highly responsive to visual stimuli during the sensitive

periods

Unique to individuals e.g. Exposure to igloo building at

a young age for eskimos