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OT 677 Environment l..> PowerPoint PPT Presentation

Describe the influence of the environment on occupational performance ... Required to match movement only to spatial features of environment ...

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OT 677 Environment l..>

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Influence of environment on visual performance l.jpg

Influence of Environment on Visual Performance


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Learning Objectives

  • Identify factors affecting the visibility of environments

  • Describe the influence of the environment on occupational performance

  • Differentiate between visual factors that facilitate occupational performance and those that impede performance

  • Analyze environments in terms of their strengths and weaknesses in visibility

  • Select appropriate environmental modification to facilitate occupational performance


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Vision is used primarily to gather information about the environment

  • Identify obstacles and threats to postural control and mobility

  • Identify the number and properties of objects to be manipulated and acted upon


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Gathering of information is completed both focally and peripherally

  • Focal perception

    • Conscious attention to specific visual information in the environment needed to complete a task

      • Example: selecting a place to sit in class

      • Vision is used deliberately and consciously for object identification and decision making

  • Peripheral perception

    • Unconscious attention to global composition of environment needed for orientation and safety

      • Example: CNS monitors verticality of walls, illumination, composition of support surface, number of obstacles

    • Information gathered allows one to remain upright in space during mobility, stay oriented and avoid collision


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Both types of perception are needed

to successfully adapt to the environment

  • Doesn’t do any good to be able to identify objects and establish a goal for movement if you can’t move toward your target without collisions

  • Ability to move and stay upright in the environment has no purpose if you don’t move in order to achieve a goal


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All environments have specific features or qualities that dictate how we can interact with them

  • Environments can be

    • Static or dynamic

    • Novel or familiar

    • Simple or complex


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Static or Fixed Environments

  • All objects in the environment are fixed in place

  • Required to match movement only to spatial features of environment

    • Can be completed visually or tactually

  • No temporal component

    • Timing is not important

  • Vision is nice but not necessary


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Dynamic or Moving Environment

  • Objects are moving independent of performer

  • Required to match movement to spatial and temporal features

    • Timing of movement is determined by external factors

      • How fast the car is approaching/when will the elevator doors close

  • Performance is dependent on speed of information processing

  • Vision plays dynamic and critical role

    • Takes you farther into environment than any other system

    • Must be combined with cognition to be effective

      • Knowing where to look for crucial information


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Familiar Environments

  • Have been in that environment before and know the layout

  • If the environment is also static, little vision is required if any

    • Navigate via kinesthetic awareness

      • Don’t have to think about the layout or where the table is-function on automatic pilot

  • Major argument for working with visually impaired older adults to “age in place”

    • Removing person from familiar environment often causes regression in performance


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Novel Environments

  • Unknown to the person

  • May also be dynamic and constantly changing

  • Requires increased use of vision and cognition

    • Most community environments fall into this category


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Simple vs. Complex Environments

  • Determined by

    • Number of objects

    • Visibility of objects

    • Placement of objects

    • Whether objects are in motion

  • Inter-plays with other qualities of environment and we often function in combinations

    • Static/simple or static/complex

    • Dynamic/simple or dynamic/complex

    • Familiar/complex or novel/complex

    • Familiar/static or novel/static


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Most Challenging Environment?


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Most Challenging Environment?

  • Novel

  • Dynamic

  • Complex


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Least Challenging Environment?


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Least Challenging Environment?

  • Familiar

  • Static

  • Simple


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Movement is Governed by Regulatory Conditions

  • Objects and features of environments with which we interact

  • Include physical and sensory properties

  • Can be facilitatory or inhibitory to performance


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Physical Regulatory Conditions

  • Nature of support surface

    • Uneven or even

    • Presence of steps, curbs, ramps etc

  • Number and nature of objects

    • Height and shape of furniture etc

    • Whether objects are in motion or static

  • Physical regulatory conditions can facilitate or inhibit travel performance

    • Well placed handrail can facilitate navigation

    • Broken pavement can increase risk of fall


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Sensory Regulatory ConditionsSound

  • Sounds can facilitate or inhibit performance

    • Sound of traffic or footfalls can assist navigation

    • Loud or irritating noise can affect concentration

    • Background noise has been shown to have a detrimental effect on speech perception by older visually impaired adults

      • Moderately noisy environments can obscure weaker speech sounds

        • Normally sighted person pays more attention to the speaker’s facial expression, posture and gestures to acquire meaning when speech is difficult to hear

        • Person with visual impairment loses that advantage-doesn’t see well enough to compensate for effects of background noise


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Sensory Regulatory ConditionsTemperature and Tactual

  • Temperature

    • Extremes in either direction (too hot or too cold) limit endurance and concentration

    • Feeling the warmth of the sun on the face can facilitate orientation

  • Tactual

    • Texture and angle of support surfaces, objects

      • Change in tactile surface can indicate curb cut, grass etc

      • Rain slicked surface or plush carpet can cause fall

    • Wind coming from a certain direction can facilitate orientation


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Sensory Regulatory ConditionsOlfactory

  • Olfactory senses are used to confirm

    other sensory input

    • Smell can assist in location of cafeteria

  • Olfaction can also inhibit performance

    • Noxious odors can be very distracting


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Visual Regulatory Conditions

  • Luminance

    • Brightness

    • Reflectance

    • Quality of light source

    • Glare

    • Even-ness

  • Background contrast

  • Background pattern

    • Static

    • Moving


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Visual Regulatory ConditionsLuminance

  • Two types of available light in environment

    • Direct

      • Windows and lights

    • Indirect

      • Reflected light off of surfaces

  • Components of illumination

    • Brightness

    • Quality of illumination

    • Presence of glare

    • Even-ness of illumination


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Brightness

  • Measured from direct source or reflectance

  • Direct source (lamp)

    • Amount of light arriving on a surface

      • Measured in footcandles

    • Power of light is measured in lumens

      • 1 lumen is equal to 1 footcandle

  • Brightness is determined by dividing the candle power of the light source by the distance of the source to the surface squared


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Light source

surface

Distance of

source

to surface

Luminance of a surface is determined by

measuring the distance between the light

source and the surface and squaring it


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Distance of source to surface 2

Then dividing it into the candle power

of the light source

Candle power of light source

Source to surface distance 2


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Footcandles can be determined using a light meter placed on the surface OR using the equation

1 lumen = 1 foot candle

**Light lumens are found on the package when you buy the

light bulb in the store

Power of light measured in lumens or

footcandles


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Brightness of Reading SurfaceExample

  • 75 watt bulb produces 1180 lumens

  • Distance to task is 3 feet

    1180 =1180 = 131 footcandles

    32 9


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Minimal Task Lighting Recommendations

  • Absolute minimum lighting (in foot candles) for an individual aged 20-29 years with 20/30 vision

    • Reading: 70

      • Telephone directory: 200

    • Seeing black thread on black cloth: 1400

    • Grooming: 50

    • Dining area: 30


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Reflectance

  • Another measure of brightness

  • Amount of illumination reflected back from the task surface to the eye

  • Measured in foot lamberts

    • Unit of brightness equal to the surface reflectance at a rate of 1 lumen per square foot


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To Measure Reflectance:

  • Can only be measured with light meter

    • Which has foot lamberts measurement

  • Hold light meter at a constant distance above the surface

  • Take reading in foot lamberts

  • Divide foot lamberts by the footcandles of the power source to get approximate % of reflectance


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Foot lamberts

Foot candles

reflectance

In foot lamberts


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2 feet

1 foot

1180

12

1180

22

=

=

295 footcandles

1180 footcandles

Brightness can be increased two ways:

1. Move the light closer to the surface


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1180

22

1710

22

=

=

295 footcandles

428 footcandles

2. Get a stronger light

75 watt

100 watt

(1180 lumens)

(1710 lumens)

2 feet

2 feet


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Quality of Light Source

  • Different types of lights give off different color wavelengths

  • Incandescent

    • Favors red end of spectrum (yellow light)

      • Less easily absorbed by retina-more glare

  • Halogen

    • Favors blue end of spectrum

      • More easily absorbed by retina-less glare

  • Full spectrum

    • All colors-pure white light

      • More easily absorbed by retina-less glare


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Presence of Glare

  • Degrades the visibility of environment

  • Two sources

    • Direct

      • Light source

      • Incandescent glares more than halogen or full spectrum

    • Indirect

      • Reflected off of surfaces: tables, floors

      • Bright shiny surfaces reflect more glare


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Even-ness of Illumination

  • Areas of shadow

    • Degrade / obscure detail in environment

  • Moving between shadow and light

    • Difficult to adjust to

      • Cones take 7 minutes to replenish

      • Rods take 1 hour to replenish


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Contrast

  • Determines visibility of objects

    • Differentiation of object from background

  • Good contrast facilitates performance

  • Poor contrast diminishes performance


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Examples of Good Contrast in Environment

Yellow lines indicate curb

Green grass line provides

shoreline border


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Examples of Inadequate Contrast

Reduced contrast obscures depth of stairs both inside and

outside of the home


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More examples of poor contrast…

Light switch blends into wall Handrail disappears


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Background Pattern

  • Created by designs and objects in environment

  • Two types

    • Moving pattern

      • Created by people, cars etc.

    • Static pattern

      • Background pattern on support surfaces

      • Inlayed or overlayed


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Moving Pattern

  • Makes it more difficult to identify target

  • More difficult to move towards the target

    • Must monitor spatial and temporal features

  • Performance depends on speed of information processing

    • Increases demand for vision and cognition


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Static Pattern

  • Types

    • Object clutter

    • Pattern inlayed in background surfaces

      • EX: Floral patterns woven into material

    • Pattern overlaying background surfaces

      • EX: shadows


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More static background pattern

Over-layed as shadow

Inlayed as part of brick/stone pattern


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Greatest challenge is a combination of

poor regulatory conditions

Example of pattern,low contrast, glare in entry way to outpatient clinic


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Pattern and Low Contrast

Shadow overlaying steps with poor contrast

Along with low contrast hand rail


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Analyzing Environments

  • Working with clients to function safely within the environment requires careful analysis of the environment

    • Reason for home visits and community outings

  • All environments have components which impede or facilitate occupational performance

    • OT job is to minimize or compensate for impediments while maximizing use of facilitators


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Impediments to Travel/Participation

  • Travel hazards

  • Fluctuating environments

  • Complex environments

  • Monochromatic environments

  • Poor and uneven illumination

  • Insufficient/poor signage


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Travel Obstacle vs. Hazard

  • Obstacle

    • An architectural or environmental obstruction in the line of travel that is easily detected and negotiated

  • Hazard

    • An architectural or environmental obstruction in the line of travel that is not easily detected


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An obstacle can become a hazard because

of poor design

Traffic lights are an obstacle

to the flow of traffic

Traffic lights are a hazard when

They can’t be easily seen


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Well marked curb cut

Invisible curb cut


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Fluctuating Environments

  • Mostly occur with community/outdoor environments

    • Rain puddles, ice, snow, nighttime

    • Indoor environments used by multiple people are an exception

  • Can create false information

    • Looks like a puddle but is really ice

  • OR obscure information

    • Shadows, pile of leaves can hide surface


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False Obscure

Overlay of shadow

creates false impression

Shadow obscures surface

of sidewalk


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Home-Messy-Home

Indoor environments can fluctuate too


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Complex Environments

  • Significantly increase cognitive load

  • Complexity directly related to amount of

    • Visual clutter

    • Moving clutter

    • Variability

Grocery store is one of the most

complex environments


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Mono environments obscure information needed for orientation


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Even-ness of Illumination

  • Areas of shadow

    • Degrade / obscure detail in environment

  • Persons with low vision report that adjusting to changing levels of illumination is the greatest challenge to mobility


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Small/Obscure Signage

  • Significantly affects orientation

  • Creates stress and limits participation

  • in environment


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Aides/Facilitators

  • Adequate/good quality illumination

  • Contrast in key structures

  • Visible safety features

  • Tactile guides to reinforce location

  • Properly placed and visible signage


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Good Quality Illumination

  • Sufficient illumination

  • Non glaring illumination

  • Even illumination


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Contrast in Key Structures

Shadow obscures sidewalk but pavement

markings facilitate navigation through the pattern


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Visible Safety Features

Dark hand railing facilitates use of low contrast stairs


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Tactual Guides

Tactual input reinforces that support surface has changed and reinforces location


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Visible Signage

Properly placed, large signage facilitates orientation


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