1. Audition and Vision

2. Exam curve
High score – 94 (average of highest and second highest scores.
90% (A) = 84.6
80% (B) = 75.2
70% (C) = 65.8
60% (D) = 56.4

3. Organization of sensory systems
Peripheral before central
Relatively more developed peripherally than centrally earlier in development
Infants are not blind or deaf at birth
By 4 to six months of age, vision and hearing are close to adultlike

4. Auditory system

5. Maturity of auditory system
External ear is small at birth, but this does not affect hearing
Middle ear cavity continues to grow during early childhood
Chain of ossicles have reached adult dimensions and rigidity by birth
Dimensions of cochlea at adult levels by 5 months gestational age.
Outermost hair cells (auditory receptors) continue to develop after birth
Auditory nerve well myelinated at birth.

6. Studies that show that infants can hear at (and even before) birth
Heart rate changes
Respiration changes
Newborns startle in response to loud noises
Cortical and brainstem ERPs
Preferential listening
Mom’s voice
Familiar song
Familiar stories

7. There are still significant differences in infants hearing from adults
In what way is infants’ hearing different from adults?
To what aspects of auditory stimuli do newborns respond differently than adults?

8. Dimensions of sound Intensity Frequency
Loudness
Frequency
Pitch
Intensity and frequency are related
Both contribute to how easily heard a stimulus is
Intensity and Frequency interact
If you hold either constant and vary the other, the sound will seem louder/quieter or higher/lower

9. Limits to the human auditory system
Relations between intensity and frequency are not linear
Audition is a very complicated system
It is possible to explore the limits of intensity and frequency

10. Intensity threshold Intensity measured in decibels
Hold frequency constant, vary intensity
Measure the intensity needed to be detected

11. Examples of decibel levels
20 dB Rustling leaves
40 dB Quiet room
80dB Lecturer
110dB Rock concert (you can feel vibrations, short term hearing loss)
180 dB Spacecraft launch

12. Intensity Thresholds Adults’ thresholds are lower than infants 5 dB
Measurements might depend on methods
Evoked potentials give lower thresholds than heartrate variability measures

13. Frequency threshold Again, depends on measures
Evoked potentials and heart rate
Reduced sensitivity in infants to high and low frequencies
Behavioral measures
Infants more responsive to high than low frequencies
Infants may respond differently to high and low frequencies
High – Orienting
Low – Arousal
With any measure, infants seem to respond ideally to the middle range, where the human voice is

14. Development in the visual system

15. Components of the visual system
Lens
Retina
Optic Nerve
Visual Cortex

16. Lens Fully Developed at birth Function: Accommodation
Ability to shift focus to different distances
Visual system can only focus on one distance at a time
To adjust to seeing at a new distance, the shape of the lens is changes
Accomplished by expanding and contracting the muscles around the eye to change the thickness of the lens
Infants do not see distance as well as adults
Originally thought to be because of immature lens
Newer studies show that they can accommodate, but they are slow and innaccurate until after about 2 months of age

17. Retina Composed of rods and cones Many more rods than cones
Most cones are in the fovea
Fovea is less mature than periphery
Cones are shorter and fatter in infants than adults until 11 months
Infants have better peripheral than foveal vision

18. Fovea development

19. Cone density in the fovea

20. Optic nerve Thinner and shorter in infants, not fully myelinated
Myelination complete by about 3 months
Peripheral-central progression
Begins at 24 weeks gestation
Length myelinated by 1 month postnatal
Dramatic increase between1 and 3 months

21. Connections between eye, lateral geniculate, visual cortex
Depends on spontaneous activity prenatally
Preventing such activity leads to abnormal connections between LGN and cortex

22. Striate (visual) cortex
Full complement of neurons and denrites are short at birth, few project
Dendritic spines proliferate after birth, peak at about 6 months
Ocular dominance columns are probably formed during this time where spines and synapses are growing then being pruned
Myelination complete after about 3 months

23. Acuity Measure of the level of detail transmitted by visual system
Optic systems work by input (stimulus) and output (vision) with a filter between
Acuity only as good as the filter
The filter is the whole visual system
How good is it?

24. Development of acuity