Sensation and Perception

There are 6 major senses vision hearing touch taste pain smell

The list can be extended with balance, joint senses and others

Vision has been studied most extensively

Transduction—physical energy to neural signal

Absolute threshold—smallest strength of a stimulus that can be detected

Difference threshold—(jnd) smallest difference that can be detected

Sensory adaptation

Purpose of the visual systemtransform light energy into an

electro-chemical neural responserepresent characteristics of objects in

our environment such as size, color, shape, and location

Light can be described as both a particle and a wave.

Wavelength of a light is the distance of one complete cycle of the wave.

Visible light has wavelengths from about 400nm to 700nm.

Wavelength of light is related to its perceived color.

The eye is like a camera; instead of using film to catch the light, we have rods and cones.

Cones allow us to see fine spatial detail and color but cannot function well in dim light.

Rods enable us to see in dim light but at the loss of color and fine spatial detail.

Our color vision is based on the presence of 3 types of cones, each maximally sensitive to a different range of wavelengths.

Auditory perception occurs when sound waves interact with the structures of the ear.

Sound Wave—changes over time in the pressure of an elastic medium (for example, air or water)

Without air (or another elastic medium), there can be no sound waves, and thus no sound.

Frequency of a sound wave is related the pitch of a sound.

Amplitude of a sound wave is related to loudness of a sound.

The frequency of a sound wave is measured as the number of cycles per second (Hertz)20,000 Hz Highest Frequency we can hear 4,186 Hz Highest note on a piano 1,000 Hz Highest pitch of human voice 100 Hz Lowest pitch of human voice 27 Hz Lowest note on a piano

ExampleP (in sound-pressure units) Log P Decibels

Softest detectable sound

Soft whisper

Quiet neighborhood

Average conversation

Loud music from a radio

Heavy automobile traffic

Very loud thunder

Jet airplane taking off

Loudest rock band on record

Spacecraft launch 9 from 150 ft.

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Purpose of the structures in the ear:Measure the frequency (pitch) of sound waves

Measure the amplitude (loudness) of sound waves

The structures of the ear transform changes in air pressure (sound waves) into vibrations of the basilar membrane.

As the basilar membrane vibrates, it causes the hairs in the hair cells to bend.

The bending of the hairs leads to a change in the electrical potential within the cell.

The way in which waves travel down the basilar membrane causes some sounds to interfere with (or mask) our ability to hear other sounds.

Low frequency sounds provide better masking than high frequency sounds.

Low frequency sounds effectively mask high frequency sounds.

High frequency sounds cannot effectively mask low frequency sounds.

Piccolo, soft

Bassoon, loud

Piccolo, loud

Bassoon, soft

Distance along basilar membrane

(a)

Distance along basilar membrane

(b)

Effect of bassoon on basilar membrane

Vibration amplitude of basilar

membrane

Vibration amplitude of basilar

membrane

Effect of piccolo on basilar membrane

Olfaction (smell)Gustation (taste)Touch and temperaturePainKinesthetic (location of body)Vestibular (balance)

Taste

• Sweet

• Sour

• Salty

• Bitter

• Umami

Pressure—Pacinian corpusclesItch—response to histamineTemperature—receptors reactive to cold or

warm, simultaneous stimulation produces sensation of hot

Pain—free nerve endings are receptors

Kinesthetic—sense of location of body parts in relation to each other

Vestibular—sense of balance, receptors located in the inner ear

Proprioceptors—receptors in muscles and joints that provide information about body position and movement

The process of integrating, organizing, and interpreting sensory information.

Some of the best examples of perceptual organization were provided by the Gestalt psychologists.

Gestalt psychologists hypothesized that “the whole is greater than the sum of the parts”.

They were interested in showing the global nature of our perceptions.

Figure-Ground Organization: Inborn part of a stimulus stands out as an object (figure) against a less prominent background (ground)

Reversible Figure: Figure and ground that can be switched

Nearness: Stimuli that are near each other tend to be grouped together

Similarity: Stimuli that are similar in size, shape, color, or form tend to be grouped together

Closure: Tendency to complete a figure so that it has a consistent overall form

Contiguity: Nearness in time and space; perception that one thing has caused another

Common Region: Stimuli that are found within a common area tend to be seen as a group

Perception is selective- we only attend to part of the sensory stimuli we receive

Seven Factors that effect Attention: Intensity Immediate Interests SizeContrastMovementIndividual NeedsIndividual Expectations

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The Ames room is designed so that the monocular depth cues give the illusion that the two people are equally far away.

Perceptual psychologists have hypothesized that the top horizontal line looks longer because it also looks farther away.

Specifically, the inward pointing arrows signify that the horizontal line is closest to you, and the outward pointing arrows signify the opposite case.

Converging lines indicate that top line is farther away than bottom line

It is hard to tell if the figure on the upper right is a trapezoid or a square slanted backward.

If we add texture, the texture gradient helps us see that it is actually a square.

The influence of prior assumptions and expectations on perceptual

interpretations