Chapter 1 Perception

Ecological Approach to Perception

James Gibson 1966, 1979

1. Perception is in “tune” with properties of the enviornment that are useful in daily life.

2. Perception comes from exploratory activities that result in awareness of the surroundings.

What are Exploratory Movements?

Movements used when listening, touching, looking snifing and so on.

Perception and Movements are a cycle: People act in order to learn bout their surroundsings and they use what they learn to guide the actions.

Sources of Perceptual Input

Looking

Listening

Touching

I would add smelling and tasting

HearingThese are the two best senses suited for perceiving things at a distance.

If you are visually impaired, hearing becomes the sole source of distance information

Events that cause sounds can be “localized” (the listener can tell what direction the sound came from)

Biaural hearing helps to localize information therefore a hearing impairment may cause an inability to localize auditory clues.

Objects can be identified by the sounds they make, the sounds they reflect, & the sounds produced from their interaction with objects such as a long cane.

Vision

Includes movement of eyes, head and body

Broad visual field allows perception of objects, spatial layout and and features of immediate surrounding

Spacial Acuity: the abiliyt to resolve small details

Contrast: dark against light (or vs. versa)

Contrast sensitivity and acuity are related by not the same. You can be functionally blind at night, yet have good acuity during the day.

Touch

Properties of the immediate surroundings:

Use pressure; vibration, temperature and pain

Incorporates relative positions and movements of the parts of the body (aka proprioception)

Also perceive information on skin from wind and sun.

The cane extends the “touch” by 3-6 feet

Environmental Flow

Follows the basic laws of gemetryTranslations – straight lines

Rotations – turns

Vision is the line of direction

Hearing provides a larger “field of view” because we can hear sounds from all directions.

Environment

Perceptual demands on non-visual street crossings have increased dramatically over the last few years (curbs to curb cuts, diesel to electric, volume (amount) of traffic, increased volume (auditory) of traffic, etc.)

Perceptual Learning

YOUR ROLE!! To provide opportunities for perceputal learning to occur

Gibson, 1969: Education of attention which leads from unskillful to skillfull perceiving, with practice and experiences

Unskillful

Requires MUCH:

attention and concentration;

Noticing both relevent and irrelevant information;

Attention to proximal information

(think beginning driver or new cane user )

Skillfull

Requires LESS attention; multitasking

Narrowing focus to relevant information

Attention to distal information

(Drivers with experience; person who travels frequently with cane)

Motor Learning

Motor learning is distinquished from perceptual learning and refers to ACQUISITION (through practice and experience)

Two components:Freedom: the dimension in which movement is free to vary. May teach student to “lock-up” degree of freedom

Automaticity: less attention required, the more automatic the skill (think day one of O&M and today!)

Perceptual Motor Coordination

Perceptual Motor Coordination is LEARNEDExample in book: knowing how far to turn when spoken to by another.

Cane use: knowing the depth of a step when explored with the cane.

Perceptual Knowledge

Pedestrian safety depends on proficiently adjusting your movements based on your perception of the environment.

Perception & knowledge are interrelated:Procedural knowledge: Knowing how and when to do things (different cane skills).

Episodic knowledge: knowing an area (increased speed w/familiarity, knowledge of environmental hazards and their location.)

Conceptual knowledge: knowledge of general patterns (layout and traffic patterns of typical intersections).

Successful O&M depends on good object-to-object relationships and self-to-object relationships.

Perceptual Errors

Detection Errors

Safe travel depends on detecting critical environmental features; the cane may miss enviornmental features

Curbs are no longer common at street corners as in the early days of O&M. (now have curb-cuts)

Stairs; Drop-offs

Ramps; inclining and declining

Study by Bentzen and Barlow (1995): 80 participants: 14/80 ramps detected slopes!

Canes and Perception

Sounds from the tap of the cane

Touch (from vibration on cane) and Sound (bimodal perception is better than auditory alone = less errors)

Techniques in use impact detecting characteristics

Dimensions of obstacles and openings

Distance from obstacles/openings

Crossing Streets w/o Vision

Street detection study: 22 different perceputal cues engaged 2 of which are ramp slope and audible traffic

Episodic and conceputal knowledge IMPORTANT for street detection

Alignment: traffic to align to trajectory, familiar features

Surge of traffic: difficult in complex intersections

Cognitive Mapping

Think about spatial layout (objects, path, streets)

Use information (ie sun)

Object-to-object spatial relationships (aka cognitive mapping)

Path integration (spatial updating): information about self-movement; maintaining orientation by the continuous processing of signals

Perceptual-Motor Coordination

Information about self-movement to knowledge of locations of objects in the environment. (walking and environmental flow)