Perception Flashcards
Threshold
Minimum stimulus that an individual can detect 50% of the time
Threshold is _____ of sensitivity
inverse
Method of ascending limits
Increase brightness until it is detected. how dark adaption occurs
Method of descending limits
Decrease brightness until cannot see any longer. Snellen VA.
Method of constant stimuli
The experimental varies the intensity randomly. Take a long time to complete
Stair step Method
Gradually increase light until deleted and then decrease until not detected. This is what is done in VF. Bracket testing
Adjust method
allows the patient to adjust the brightness.
Patients with strict criteria
will not indicate they see a light until absolute certain. Will have false high thresholds
Patients with lax criteria
will hit whenever they think they may have seen it. Will have lower than expected thresholds. False positives.
Threshold for forced choice
75%
Signal detection theory
How a patient picks signal from background noise. The more separated S is from S+N the easier to detect.
Sensitivity
TP/TP + FN (population with disease)
Specificity
TN/TN+FP (population with/o disease)
Positive Predictive Value
Probability patient has disease if test is possible. TP/TP+FP
Negative Predictive Value
Probability patient doesn’t have disease if test is negative. TN/TN+FN
Receiver Operating Characteristic Curve
How a patients criteria affects the detectability of the signal. Lax will be up on to right. Strict will be low on the left.
Radiometry
Energy per time produced by a source of electromagnetic radiation.
Radiant power
The energy per second produced by a light source
Radiant Intensity
Energy per second in a given direction
Radiance
Like a megaphone of projected light
Irradiance
Light on a surface
Photometry
How our visual system detects electromagnetic radiation.
Luminous power
Visual systems response to light. Higher lumen=higher response=higher perception of brightness.
Luminous efficiency function
V=1 is the brightest and V=0 is the least bright
When does V=1 with photopic system
555 nm with 680 lumens/watt.
When does V=1 for scotopic system
507 with 1700 lumens/watt
Abney’s law of additivity
Can ad the V’s together if more than one wavelength in a light
Narrow band filters
Only allow a small range of wavelengths to pass through. Location of peak specifies which can pass and half-height bandwidths-A higher number=less sensitive.
Half height bandwidth
Larger number=less sensitive
Interference filters
Highly sensitive (low half height bandwidth) that only transmit a single wavelength
Broad band filters
allow a wide range of filters
Long pass filters
Transmit only long wavelengths. Change color perceptions.
Neutral density filters
Transmit all wavelength equal so no change in color perception. Will decrease light transmitted to eye and therefore will have a slower neural response
Pulfrich Phenomenon
Pendulum moves in an circle instead of back and forth. Over left=clockwise. Over right=counterclockwise.
Lambert surface
Surface that shows the same luminance in every angle or scatters light equally in all directions. ie. matte paper.. L=RE. If Luminance is doublbled so will L
Specular Surface
Surface that unequally scatters light. i.e. shinny piece of silver.
Retinal Illumination
T=LA. L=luminance A=area of pupil.
Scotopic vision
Poor visual acuity, lack of color discrimination, good sensitivity but poor resolution.
Photopic vision
Good VA, good color, poor sensitivity but good resolution (think amount PR to ganglion)
Mesopic conditions
when both rods and cones are active
Principal of Univariance
Although wavelength of photon affects its absorption, once it is absorbed all facts about it are lost.
When is photo chromatic interval zero
650 nm. Both are equally sensitive.