Topic 1

• Information is sent/received

  through...

  ▪ visual, auditory, haptic, movement
• Information stored in memory

  ▪ sensory, short-term, long-term
• Two stages in vision

  VISION

  ▪ physical reception of stimulus

  ▪ processing and interpretation

  of stimulus
• The Eye - Physical

  Reception

  • mechanism for receiving light and transforming it into

  electrical energy

  • light reflects from objects

  • images are focused upside-down on retina

  • retina contains rods for low light vision and cones for

  color vision

  • ganglion cells (brain!) detect pattern and movement
• Size and depth

  • visual angle indicates how much of view object

  occupies (relates to size and distance from eye)

  • visual acuity is ability to perceive detail (limited)

  • familiar objects perceived as constant size (in

  spite of changes in visual angle when far away)

  • cues like overlapping help perception of size

  and depth
• Brightness

  • subjective reaction to levels of

  light
• Color

  • made up of hue, intensity,

  saturation
• The visual system compensates for:

  • movement

  • changes in luminance

  • Context is used to resolve ambiguity

  • Optical illusions sometimes occur due to

  overcompensation
• Optical Illusions an illusion caused by the visual system and

  characterized by a visual percept that

  (loosely said) appears to differ from reality.

  • Kinds of Visual Illusions

  ∆ Ambiguities

  ∆ Distortions

  ∆ Paradoxes

  ∆ Fictions
• Ambiguities

  there are hidden objects,

  which can be revealed by

  looking at the images from

  a specific point of view
• Distortions

  the perceptions of

  size, shape, color

  and orientation get

  severely distorted
• Paradoxes

  depict objects which

  initially seem normal,

  but in reality, cannot

  exist
• fictions

  the perception of objects

  that are genuinely not

  there to all but a single

  observer. These are

  more properly called

  hallucinations.
• Reading

  Several stages:

  o visual pattern perceived

  o decoded using internal representation of language

  o interpreted using knowledge of syntax, semantics,

  pragmatics

  • Reading involves saccades and fixations

  • Perception occurs during fixations

  • Word shape is important to recognition

  • Negative contrast improves reading from computer screen
• Important Terms:

  • Syntax - the arrangement of words and phrases to create

  well-formed sentences in a language.

  • Semantics - the branch of linguistics and logic concerned

  with meaning.

  • Pragmatics - the branch of linguistics dealing with language

  in use and the contexts in which it is used (how context

  contributes to meaning).
• Hearing Provides information about environment:

  • distances, directions, objects etc.

  • Physical apparatus:

  o outer ear - protects inner and amplifies sound

  o middle ear - transmits sound waves as vibrations to inner

  ear

  o inner ear - chemical transmitters are released and cause

  impulses in auditory nerve
• touch Provides important feedback about environment.

  • May be key sense for someone who is visually impaired.

  • Stimulus received via receptors in the skin:

  o Thermoreceptors - heat and cold

  o Nociceptors - pain

  o Mechanoreceptors - pressure

  • Some areas more sensitive than others e.g. fingers.

  • Kinesthesis - awareness of body position affects comfort and

  performance.
• Movement

  Time taken to respond to stimulus:

  reaction time + movement time

  • Movement time dependent on age, fitness etc.

  • Reaction time - dependent on stimulus type:

  o visual ~ 200ms

  o Auditory ~ 150ms

  o Pain ~ 700ms

  • Increasing reaction time decreases accuracy in the unskilled

  operator but not in the skilled operator.