Basic Visual Functioning

1. Basic Visual Functioning

2. Basic Visual Functioning • The processing of information, through perception and cognition, undergoes rapid development in infancy • The limiting factor for the input to the information processing system is sensory processes that extract information • These sensory processes can be related to the developing nervous system

3. Basic Visual Functioning • Vision works by processing information about the spatial environment • So we will look at the following aspects of spatial vision • Acuity and contrast sensitivity • Orientation selectivity • Eye movements

4. Adult Basic Visual Functioning: Visual Acuity • Tested with preferential looking and VEP • VEP gives better acuity measures than looking • Trend is the same, however Preferential Looking

5. Adult Basic Visual Functioning: Visual Acuity • Tested with preferential looking and VEP • VEP gives better acuity measures than looking • Trend is the same, however VEP

6. Development of Visual Acuity

7. Basic Visual Functioning:Visual Acuity • Acuity levels off after 6 mos. and reaches adult level by 1 year

8. Basic Visual Functioning:Contrast Sensitivity • Differs from acuity in that it is concerned with the amount of brightness difference between light and dark regions

9. Basic Visual Functioning:Contrast Sensitivity • Differs from acuity in that it is concerned with the amount of brightness difference between light and dark regions

10. Basic Visual Functioning:Contrast Sensitivity • Overall sensitivity increases in early infancy • Peak sensitivity shifts to higher spatial frequencies (finer details) • Higher spatial frequencies are detectable

11. Basic Visual Functioning:Acuity & Contrast Sensitivity • What accounts for their development? • Cone density in fovea is 1/3 of adult’s • Cone length is 1/10 of adult’s 1 month cone density 6 month cone density

12. Basic Visual Functioning:Acuity & Contrast Sensitivity • What accounts for their development? • Lens does not accommodate to changes in distance • The axons of retinal ganglion cells, which form the optic nerve, have myelin sheath that is still developing • The lateral geniculate in the visual cortex continues to develop and progressively responds to higher frequencies (finer detail)

13. Basic Visual Functioning:Orientation Selectivity • Acuity and contrast sensitivity give only the pattern of light and dark in the image of the world • In order for this information to be useful, the system must extract significant properties • Evidence suggests that processing in the early visual cortex is organized into groups of neurons that selectively respond to a particular pattern

14. Basic Visual Functioning:Orientation Selectivity • One such selective pattern is orientation of the light and dark distribution in the image • Braddick, Wattam-Bell, & Atkinson (1986) used visually evoked potentials (VEP) • Simply switched the orientation of a stripe pattern and measured brain activity Sequence Phase Shift Orientation Shift Phase Shift Phase Shift Phase Shift

15. Basic Visual Functioning:Orientation Selectivity • Braddick, Wattam-Bell, & Atkinson (1986) found that the VEP changed exclusively at the orientation shift by 6 weeks of age • Maurer & Martello (1980) have shown that behaviourally, via habituation, that 6-wk-olds will discriminate these orientation changes. Sequence Phase Shift Orientation Shift Phase Shift Phase Shift Phase Shift

16. Basic Visual Functioning:Orientation Selectivity • Slater (1989), using novelty-preference, found evidence of orientation discrimination in newborns

17. Basic Visual Functioning:Eye Movements • There are two types of eye movements • Saccades: Localize stationary objects • Pursuit: Track moving objects

18. Basic Visual Functioning:Eye Movements • Saccades • By 1 month, infants can localize intended targets • However, they are not very accurate and are relatively slow • Becomes more adult-like by around 6 months of age • By 3 months, infants can make predictive saccades

19. Basic Visual Functioning:Eye Movements • Saccades • Canfield, Smith, Brezsnyak, & Snow (1997) studied the stability of infants’ saccade latency • Adults’ typical minimum latency is approximately 133 milliseconds

20. Basic Visual Functioning:Eye Movements • Pursuit • Aslin (1981) did the most detailed study of pursuit • Very difficult to detect in infants younger than 2 months of age • They make many saccades to track • By 6 months, they are able to track reliably, as does an adult

21. Basic Visual Functioning:Eye Movements • Pursuit • However, Phillips, Finocchio, Ong, & Fuchs (1997) have found that even younger than 2 months will exhibit smooth pursuit if target is moving slowly (10 degrees per second) • Percentage of time actually tracking, even at slow speeds, also increases up to 6 months

22. Visual Attention • Eye movements, as well as processing resources, need a target for them to be implemented • So, attention needs to select a target in the environment • Infant procedures, habituation and novelty-preference, tap into the attention mechanisms because they measure the amount of time infants selectively look at one stimulus versus another

23. Visual Attention • Cohen (1972) suggested two components to performance on the looking tasks: • Attention-Getting and Attention-Holding • So he measured latency to fixate and duration of fixation to checkerboard patterns

24. Visual Attention • Checkerboard size influenced latency • Number of checks influenced duration

25. Visual Attention • Cohen suggests that after the attention-getting phase there is an attention-holding phase, during which processing of the stimulus event occurs • Richards (1988, 1991) measured heart-rate change to assess whether infants are in fact actively processing during attention-holding

26. Richards (1988, 1991) • Richards found that during attention-holding, which he called “sustained attention”, heart-rate decelerated • Also found that infant is less likely to be distracted by a second stimulus when in heart-rate deceleration • Kagan found that this heart-rate deceleration showed a more systematic decline across stimulus repetitions with age Pre-Attention Attention Termination Orienting Sustained Attention

27. Selective Attention • Visual Pop-Out • Stimuli with a unique property jump out from the surrounding environment and capture our attention • Sireteanu & Rieth vs. Atkinson & Braddick (1992) - used preferential looking to assess pop-out in infants

28. Selective Attention • Sireteanu & Rieth found that 10 to 12-month-olds exhibited pop-out • Atkinson & Braddick found that 3.5 to 4.5-month-olds exhibited pop-out