Influence of environment on visual performance
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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

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

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

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

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

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

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

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

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

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

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

Most Challenging Environment?

Most Challenging Environment?

  • Novel

  • Dynamic

  • Complex

Least Challenging Environment?

Least Challenging Environment?

  • Familiar

  • Static

  • Simple

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

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

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

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

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

Visual Regulatory Conditions

  • Luminance

    • Brightness

    • Reflectance

    • Quality of light source

    • Glare

    • Even-ness

  • Background contrast

  • Background pattern

    • Static

    • Moving

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


  • 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

Light source


Distance of


to surface

Luminance of a surface is determined by

measuring the distance between the light

source and the surface and squaring it

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

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


Brightness of Reading SurfaceExample

  • 75 watt bulb produces 1180 lumens

  • Distance to task is 3 feet

    1180 =1180 = 131 footcandles

    32 9

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


  • 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

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

Foot lamberts

Foot candles


In foot lamberts

2 feet

1 foot







295 footcandles

1180 footcandles

Brightness can be increased two ways:

1. Move the light closer to the surface







295 footcandles

428 footcandles

2. Get a stronger light

75 watt

100 watt

(1180 lumens)

(1710 lumens)

2 feet

2 feet

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

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

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


  • Determines visibility of objects

    • Differentiation of object from background

  • Good contrast facilitates performance

  • Poor contrast diminishes performance

Examples of Good Contrast in Environment

Yellow lines indicate curb

Green grass line provides

shoreline border

Examples of Inadequate Contrast

Reduced contrast obscures depth of stairs both inside and

outside of the home

More examples of poor contrast…

Light switch blends into wall Handrail disappears

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

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

Static Pattern

  • Types

    • Object clutter

    • Pattern inlayed in background surfaces

      • EX: Floral patterns woven into material

    • Pattern overlaying background surfaces

      • EX: shadows

More static background pattern

Over-layed as shadow

Inlayed as part of brick/stone pattern

Greatest challenge is a combination of

poor regulatory conditions

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

Pattern and Low Contrast

Shadow overlaying steps with poor contrast

Along with low contrast hand rail

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

Impediments to Travel/Participation

  • Travel hazards

  • Fluctuating environments

  • Complex environments

  • Monochromatic environments

  • Poor and uneven illumination

  • Insufficient/poor signage

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

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

Well marked curb cut

Invisible curb cut

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

False Obscure

Overlay of shadow

creates false impression

Shadow obscures surface

of sidewalk


Indoor environments can fluctuate too

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

Mono environments obscure information needed for orientation

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

Small/Obscure Signage

  • Significantly affects orientation

  • Creates stress and limits participation

  • in environment


  • Adequate/good quality illumination

  • Contrast in key structures

  • Visible safety features

  • Tactile guides to reinforce location

  • Properly placed and visible signage

Good Quality Illumination

  • Sufficient illumination

  • Non glaring illumination

  • Even illumination

Contrast in Key Structures

Shadow obscures sidewalk but pavement

markings facilitate navigation through the pattern

Visible Safety Features

Dark hand railing facilitates use of low contrast stairs

Tactual Guides

Tactual input reinforces that support surface has changed and reinforces location

Visible Signage

Properly placed, large signage facilitates orientation

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