Human Factors Exam 2

Accommodation Measurements

1. Perceptual 2. Objective

Torsional Movements Measurements

1. Search Coil 2. Image processing/ Correlation Methods

What are the physiological events of high noise dosage?

1. Short Term Effects • Startle response 2. Long Term Effects ( >95 dBA, > 10 yrs) • Hypertension • Hypotension • Ulcers • Headaches • Irritability • Sleep disorders • and so on...

What are some ways to reduce the effects of masking?

1. Signal Control - Selection: Distinction from noise - Intensity: Above masked threshold 2. Noise Control - Selection: distinct from signal - intensity: reduce - filter: alter spectrum to reduce masking 3. Binaural Hearing

Characteristics of OKN

1. Slow phase associated with fixating a portion of moving pattern and following with a pursuit eye movement 2. Fast phase associated with saccadic eye movement that returns eyes to original starting point 3. Minimum time between fast phases is about 200 msec, time between slow phase is longer 4. Amplitude generally from one degree to ten degree 5. Amplitude can be reduced considerably by placing stationary fixation point within visual field

What is complex sound and how are they relatively insensitive to pitch changes when they are from musical instruments?

1. Sum of pure sinusoidal tones 2. Because they are insensitive to pitch changes that are resulting from changes in sound intensity

Noise control

1. Use of barriers 2. Baffles 3. Enclosure 4. Ear protection (Ear plugs, mufflers, active noise reduction)

What are some hearing tests?

1. Whisper tests 2. Clock/ Watch tick test 3. Audiometer

Characteristics of EOG

1.Cornea is positively charged with respect to the retina due most likely to the higher metabolic rate of the retina 2. The 1 mV (CFP) difference between the cornea and retina can be treated as a rotating dipole 3. Theoretically, the change in voltage is related to the sine of the eye position angle 4. Recorded signals range from approximately 15 to 200 mV 5. Eye movements up to ±70° with sensitivity about 4mV/deg 6. Accuracy 0.5° to 2°

Photoelectric Characteristics

1.Differential measurement of reflected light between the iris and scleral boundaries 2.Linearity limited to approximately ±15° 3. With stabilized head, accuracy to better than 0.1° 4.Vertical measurement is often indirect 5. Must compensate for cross-talk 6. Analog output

Range of Hearing

20- 20 kHz

When is there no TTS2

70 to 75 dBA

When is TTS2 proportional to exposure?

80 to 105 dBA

What happens with noise induced hearing loss?

A notch develops at about 4 kHz which continues to deepen (further loss of hearing) and widen (from 3 to 6 kHz) with continuing noise exposure With each, the loss is permanent

Sones

A scale that relates the physical intensity to the psychological experience of loudness

Spontaneous (Or gaze) nystagmus

Associated with any one of a number of neurological disorders and is often associated with a particular eye position

Auditory vs Visual Displays 1. Message Length 2. Response 3. Localization 4. Operator Loading 5. Info Rate 6. Coding 7. Attention- getting 8. Directed attention

Auditory 1. Short 2. Immediate 3. Limited 4. High Visual 5. Low 6. May be Simple 7. Good 8. Not required Visual 1. Long 2. Later 3. Good 4. High auditory 5. High 6. Often complex 7. Limited 8. Required

What does the potential of any auditory signal to be masked depend on?

Both the intensity (power) and frequency of that signal

Smooth Pursuit Movements

Conjugate movements used to track slowly (1 to 30 degrees per second) moving targets in order to stabilize an image of the moving target on the retina

Temporary Hearing loss

Continuous noise leads to hearing loss. Temporary threshold shift at 2 min (TTS2)

Vergence eye movements

Disjunctive movements in response to changes in target depth. Can be either convergence or divergence of the eyes

Psychophysical Scaling

Equal increases in sound intensity do not result in equal increases in loudness

What is the effect of frequency on JNDs?

From low to midrange frequencies, smaller frequency differences are detectable with increasing sound intensity

Tremor

High frequency tremor (30 to 150 Hz) of the eyes during normal fixation. Peak amplitudes are on the order of 30 arc seconds at 70 Hz.

Photoelectric (Limbus)Techniques

Involve measuring changes in the amount of infrared light reflected from the surface of the eye as it moves relative to the light source.

Boundary reflection (Purkinje image) Techniques

Involve monitoring the relative positions of the reflections of a light source from various boundary surfaces within the eye. For instance, in the most simple corneal-reflection implementation, eye position is measured by determining the angle between the reflected light and the normal to the cornea. The corneal reflection moves in the direction of eye movement. The reflex moves roughly half as much as the eye.

What happens with low intensity masking tones (20 to 40 dB) to the masking effect?

It is confined to a narrow band of frequencies.

What happens with high intensity masking tones (60 to 100 dB) to the masking effect?

It spreads to higher frequencies

Just Noticable Difference (JND)

Least change in a stimulus or the least difference between two stimuli that can be detected 50% of time

Characteristic of Pupil/Corneal Reflection

Less Sensitive to translation

What type of sounds can mask high pitch sounds easier than the converse?

Low pitch.

What does fixation due for the eyes?

Minimizes retinal error, allows for maximum extraction of visual information

Dimension 1. Intensity 2. Frequency 3. Duration 4. Intensity and Frequency

Number of Levels 1. 4 to 5 2. 4 to 7 3. 2 to 3 4. 9

Noise Dosage

Partial dose equals time at sound level over maximum time allowed at sound level Total (daily) dose = sum of partial doses Requirement: total dose is less than or equal to 1

What are the psychophysical indices of loudness?

Phon and Sone

What is the hearing pathway?

Pinna -> Auditory Canal -> Tympanic Membrane -> Ossicles -> Oval Window-> Cochlea -> Auditory Nerve -> Auditory Cortex

What is the difference between pitch and frequency?

Pitch is a perceptual sensation while frequency is a physical measurement

Intensity

Pressure amplitude

Optokinetic nystagmus

Produced by a moving visual field containing repeating patterns

Loudness

Psychological experience that correlates but is not identical to the physical measurement of sound intensity

Saccadic Eye Movements

Rapid, Conjugate Movements by which fixation or eye position is voluntarily changed from one point to another

Pupil/ Corneal reflection Techniques

Represent an improvement of the corneal reflection techniques whereby eye position is estimated by taking the scaled differences between the pupil center and the location of the corneal reflection.

Torsional eye movements

Rotational eye movements about the line of sight

Sound

Sensed variations due to compression and expansion/ rarefaction of air molecules. Change in pressure

Vestibular nystagmus

Similar to optokinetic nystagmus in appearance, but is in response to simulation of semicircular canals during rotation of the head

Drift

Slow random movement of the eye away from the target at velocities approaching several arc minutes per second

Microsaccades

Small rapid eye movements with amplitudes of several arc minutes up to one degree separated as little as 30 msec. Dynamic properties are similar to those of larger amplitude saccades in term of peak velocity and accelerations

What is the Effect of Sound Pressure Level on JNDs?

Smaller JNDs occur when: 1. The frequencies fall within the optimal hearing range 2. The sound pressure level above threshold is increased

What is the effect of Duration on JNDs?

Smaller JNDs occur when: 1. the duration of the sound is increased 2. The frequency of the sound source is decreased

Miniature (or fixation) eye movements

Smaller than one degree in amplitude and serve to make minor corrections to the fixation point

Compensatory eye movements

Smooth movements, but compensate for active or passive motion of the head or trunk

Where else can sound enter besides the outer ear?

Sound can also enter the hearing pathway through bony conduction. Must be 30-50 dB. Delay effects because of bony conduction

What are compensatory eye movements thought to be attributable to?

Stimulation of the semicircular canals due to head turning and to stimulation of proprioceptors located in the neck

Pitch

Subjective perception of highness or lowness of a tone

What is the size of the critical band a function of?

The center frequency. The higher the frequency, the larger the critical band

What does each curve represent on a perceived loudness scale?

The intensity levels of various frequencies that are judged by an observer to be equally loud

What is the primary concern in the masking of pure tones by a wideband noise?

The intensity of the masking noise in a critical band around the frequency of the masked tone.

Electrooculography (EOG)

The measurement of the electrical potential between surface electrodes placed around the eye. The eye is an electrical dipole that is more positive at the front than at the back [this results in the so-called corneal-fundal potential (CFP)]. Therefore, when the eye moves the potential between the surface electrodes changes.

What can masking be influenced by?

The nature of the masking sound ie. if it is Pure, Complex, or Noise

What is the purpose of compensatory eye movements?

To stabilize retinal image of fixed objects during head motion

True/False. Consonant sounds are more vulnerable to masking than vowels.

True. They are.

Noise

Unwanted Sound Auditory information carrying no information relevant to the current task

Can sounds be masked by other sounds?

Yes, the threshold for one sound can be raised by the presence of another sound

What is the minimum sound intensity difference so a sound can be heard above a mask?

about 15 dB

Direct contact lens systems (search coils)

involves measuring the movement of a coil, attached to the eye, relative to an external magnetic field.

Artifacts of EOG

• EMG, EKG Interference • Changes in baseline CFP (e.g., due to diurnal, hormonal, adaptation factors) • Changes in electrode potential • Cross coupling • AC or DC coupling • Frequency response limited to less than 130 Hz

Design/Selection Principle of Things featuring Auditory Features

• Method of Presentation • avoid extremes of dimensions (not too high or not too low) • relate intensity to ambient noise levels • consider ambient acoustic environment • use interrupted / variable signals • should be unique from other stimuli (disassociability) • have consistent meaning (invariance) • require very few assumptions in terms of meaning - present in its simplest form possible (parsimony) • don't overload with auditory stimuli • utilize learned / natural relationships • Installation • test before use • avoid conflict with previously used signals • facilitate change-over

What is the Applicability of Auditory Displays?

• Signal originates as sound • Raw, un-encoded signals • Simple, short messages • Verbal messages • Immediate action required • Visual overload • Poor visual conditions • Impaired vision • Receiver moves about

Acoustic or Aural Reflex

• Stapedius muscle contracts resulting in reduced sound transmission to the inner ear • Reaction time 35 to 150 ms before contraction • Provides approximately 20 dB of sound attenuation • Reflex lasts between 2-3 seconds • Can maintain for 15 min - if high intensity noise persists • Sensitive to broadband frequency content and if 80 dB above threshold

Threshold of Hearing

0 dB (20 MicroPascals)

Phons

1 phon is equal to 1 dB of loudness of a 1 kHz tone, a standard calibration value 40 phons equals 1 sone and every additional phons doubles the number of sones

What frequency are tones relatively insensitive to intensity induced pitch changes?

1 to 2 kHz (For frequencies greater than 2 kHz, pitch increases with increasing amplitude) (For frequencies less than 1 kHz, pitch decreases with increasing amplitude)

Highest Sensitivity

1 to 3 kHz

Characteristics of Torsional eye movements

1. Amplitudes generally less than 10 degrees 2. May be produced by optokinetic nystagmus or vestibular stimulation caused by head rotation or tilt

Two Methods of Pupil/Corneal Reflection

1. Bright Pupil Method 2. Dark Pupil Method

What are some characteristics from vergence eye movements?

1. Can be elicited in accommodation as well a binocular disparity 2. Dynamics are much slower than those of the pursuit system 3. Maximum velocity is about 10 degrees per second for a 15 degree eye movement

Subcategories of miniature eye movements

1. Drift 2. Microsaccades 3. Tremor

What can the ability to distinguish between two stimuli or sounds be based upon?

1. Frequency- Pitch 2. Intensity- Loudness 3. Spectrum Characteristics 4. Phase Differences

Saccadic Attributes

1. High initial acceleration and deceleration up to 40,000 degrees per second squared 2. Peak velocity 400 to 600 degrees per second 3. Duration dependent on amplitude, varies between 30 to 120 ms 4. Response latency between 100 and 300 ms 5. Head movement occurs when target is greater than 30 degrees

Characteristics of Direct Contact Lens

1. Highly accurate on the order of several arc seconds 2. Lenses subject to slip 3. Require topographical anesthetic 4. Cannot be used for extended periods 5. Analog output

Non-continuous noise

1. Impact noise 2. Impulse noise May lead to PERMANENT Hearing loss

Binaural Hearing

1. Increases sensitivity (14 to 16 db) 2. Sound localization 3. Masking reduction

Pupillary Size/ Response Measurements

1. Infrared Photoelectric 2. Two-dimensional image analysis

Boundary reflection Characteristics

1. Limited to approximately ±15° 2. Range can be increased with linearization or by adding additional corneal reflections 3. Highly sensitive to translation

Smooth Pursuit Attributes

1. Not under voluntary control, requires some form of moving visual field or target 2. Velocities up to 100 degrees per second 3. Latency of pursuit system at 130 ms, less than saccades 4. Predictor operator minimizes phase lag during tracking