Sensation and Perception

S and P

Introductory Concepts

24-7 stimuli from the outside world bombard us. How do we construct our

representations of the outside world?

• Sensation: the activation of our senses– In the body – the eye,

the ear, the nose, etc. – collects external information

– Data entry

• Perception: the process of interpreting the sensory info and understanding it– In the brain

S and P

• In our everyday experience, S and P blend into a continuous process. It’s a fine line where one stops and the other begins

• Transduction: the point where S stops and P begins. The point at which a part of the body fires the info to the brain– Optic nerve – vision– Auditory nerve – hearing– Olfactory bulb - smell

Bottom Up Processing

• Sensory analysis starts at entry level – bottom up from the senses to the brain.

• We do not use our past experiences to make a judgment. Instead we wait until we have all of the info to build a complete and accurate perception.

• Bottom up is slower but more accurate

Top Down Processing

• Sensory analysis based on our past experience and expectations

• We use our Schema (expectations of how we anticipate the world to be) to fill in the gaps and make a judgment before we have all the required info. Our schema predispose us to experience the world in a particular way

• Top down is faster, but more prone to error– Ex: I ope yo et a 5 on t AP e am.– Ex: seeing images in a cloud

Top Down Processing

• I cnduo't bvleiee taht I culod aulaclty uesdtannrd waht I was rdnaieg. Unisg the icndeblire pweor of the hmuan mnid, aocdcrnig to rseecrah at Cmabrigde Uinervtisy, it dseno't mttaer in waht oderr the lterets in a wrod are, the olny irpoamtnt tihng is taht the frsit and lsat ltteer be in the rhgit pclae. The rset can be a taotl mses and you can sitll raed it whoutit a pboerlm. Tihs is bucseae the huamn mnid deos not raed ervey ltteer by istlef, but the wrod as a wlohe. Aaznmig, huh? Yaeh and I awlyas tghhuot slelinpg was ipmorantt! See if yuor fdreins can raed tihs too.

Thresholds – what stimuli do we detect? At what intensity? Do we notice change in a

stimuli?

• Absolute threshold: the smallest amount of a stimuli we notice 50% of the time

• Subliminal messages: below the 50% AT.

Absolute Threshold

Signal Detection Theory

• Our ability to detect a signal depends not only on the strength of the signal but also on our personal response criteria – our experiences, expectations, motivation, alertness, etc.– Will the doctor see the tumor on the CAT

scan?– Will the parent hear the baby crying?– Will the QB see the open receiver in the end

zone?

Perceptual Mistakes

False Positive: We think we perceive a stimulus that isn’t there

Ex: the doctor tells the patient that have cancer, but they don’t

Ex: the parent runs to get the crying baby but the baby is asleep

False Negative: we miss a stimulus that is present

Ex: the doctor gives the patient a clean bill of health but they have a small tumor

Ex: the baby is crying and the parent doesn’t hear it

Difference Thresholds – how much does a stimulus need to change for us to notice?

• Just Noticeable Difference (JND) – once we are aware of a stimulus it’s the smallest change needed for us to notice

• Weber’s Law: JND is proportional to the size of the original stimulus. The louder, brighter, bigger the initial stimulus the greater the JND

Sensory Adaptation

• Diminished sensitivity to an unchanging stimulus

– I walk into the house and smell fresh baked cookies, but after a few minutes don’t notice the smell

– I get into a cold pool but after a bit I adjust and the water no longer feels cold

Selective Attention

• https://www.youtube.com/watch?v=Ahg6qcgoay4

• How many times does the white team pass the ball?

• Inattentional Blindness – failing to see visible objects when our attention is directed elsewhere

• Take away – be aware of cyclists, pedestrians, and don’t text and drive

• Your 5 senses take in 11,000,000 bits of info per second. You consciously process about 40 bits. We choose what to attend to

• Ex - Cocktail party effect:Your ability to attend to only

one voice among many – focused listening – you hear your name among the backdrop of lots of conversations

Ex – R/L hearing

Prosopagnosia – face blindness – Sensation without Perception

• Can be caused by brain damage to fusiform gyrus in temporal lobe (Right brain)

• 6o Minutes Clip – Face blindness –

https://www.youtube.com/watch?v=dxqsBk7Wn-Y

VISION

• Vision, hearing and touch= energy senses–We gather energy from light, sound waves and pressure

• Taste and smell = chemical senses

Vision = our most dominant sense• Step 1: gather light

–Light is reflected off objects and gathered by the eye.

–Visible light = small sections of the electromagnetic spectrum

The Color we see depends on . . .

1. Light intensity–How much energy the light contains

determines the brightness–Energy is determined by the wave’s

amplitude/height–The higher the amplitude, the

brighter the color; the lower, the duller

The Color we see also depends on

2. Light wavelength–Determines hue (color)–Wavelength = peak to peak–Wavelengths longer than visible light–High frequency (short wave length) =

purples and blues–Low frequency (long wave length) =

oranges/reds

Properties of a wave – amplitude and frequency

Visual Spectrum

Step 2: Within the eye1. Reflected light enters through the cornea

2. Light passes to the pupil. Muscles that control the pupil (iris) open it (dilate) to let more light in and make it smaller to let less light in

3. Light that enters the pupil is focused by the lens

4. As light passes through the lens, the image is flipped upside down and inverted and projected onto the retina. The retina is like a screen at the back of the eye.

Within the Retina – a series of nerves fires to ultimately send the image to the brain – layer 1 =

rods and cones

CONES• 6 million

• Center of retina – our central vision

• Sees color

• Detailed vision in daytime

• Not sensitive in dim light

RODS• 120 million

• Peripheral vision

• Black and white – no color

• Good vision at night

• Very sensitive in dim light

Within the retina….

• 2nd layer of cells = bipolar cells• 3rd layer of cells – ganglion cells

– Axon of the Ganglion cell is the optic nerve. The optic nerve sends the info to the thalamus to the occipital lobe for perception to take place in the brain. The occipital lobe processes the image – left occipital processing images from the right visual field.

– The point at which the optic nerve leaves the eye causes a blind spot.

Blind Spot

Theories of Color Vision

• There are competing theories of how and why we see color

Trichromatic• Oldest and most simple theory• Says we have 3 types of cones in

the retina that detect blue, red and green

• These cones are activated in different combinations to produce all the colors of the visual spectrum

Problems with Trichromatic

• Can’t explain afterimages–green/red; blue/yellow, black/white

• Or colorblindness–Can’t distinguish between red/green or blue/yellow and can only see shades of gray

Color Blind Test – CB people typically don’t see shades of red

and green

Afterimage

Opponent Process Theory• The sensory receptors arranged

in the retina come in pairs –Red/green; blue/yellow; black/white

• If one sensor is stimulated, the pair is inhibited from firing

Opponent Process Theory explanations• Afterimages: if you stare at red long

enough then you tire the sensors, therefore when you look at a blank page, the opponent to red, green, will fire and you will see a flash of green

• Colorblindness: pairs explain why you can’t see both hues – the red/green pair is dysfunctional

HEARING

Hearing also uses energy in the form of waves; sound waves; vibrations in the air are collected by the ear. Vibrations go through the process of transduction where they are converted into neural messages and sent to the brain.

Sound Waves

• 1.) Amplitude – height of wave, determines loudness of sound– Measured in decibels– The higher the

amplitude the taller the wave the louder the sound

– Prolonged exposure to 85 decibels or higher causes damage and hearing loss

Sound Waves cont . . .

2. Frequency = length of waveDetermines pitch (measured in megahertz)

Higher pitched sounds have higher frequencies, waves are densely packed together and speed by quickly

Process of HearingSound waves are collected in the outer ear. Then travel down the ear canal (auditory canal) until they reach the ear drum (the thin membrane that vibrates as sound waves hit it.) The eardrum is attached to first in a series of three small bones – the hammer, anvil, and stirrup

Process of HearingThe vibration of the eardrum is transmitted by these three bones to the oval window (a membrane similar to the eardrum)

The oval membrane is attached to the cochlea (a structure shaped like a snail’s shell and filled with fluid.)

The floor of the cochlea is lined with hair cells which are connected to neurons

Process of Hearing cont . . .When the fluid moves, the hair cells move and transduction occurs- the neurons fire and these impulses are carried to the brain by the auditory nerve (to the temporal lobes of the brain)

Hair cells are extremely sensitive and quick . . . damage to hair cells account for most hearing loss. Once they are damaged, they do not regenerate. Prolonged exposure to loud sounds (85 decibels +) damages hair cells (ringing in your ears)

Pitch TheoriesPlace Theory: the hair cells in the cochlea respond to different frequencies of sound based on where they are located in the cochlea (like a choir). Some bend in response to high pitches and some to low. We sense pitch because the hair cells more in different places. (Accurately describes how hair cells sense higher pitch, not lower ones.

Pitch Theories cont . . . Frequency Theory: Lower tones are sensed by the rate at which the cells fire. We sense pitch because the hair cells fire at different rates (frequencies) in the cochlea (explains low pitch).

Deafness

Conduction deafness: when something goes wrong with the system of conducting the sound to the cochlea (in the ear canal, eardrum, hammer/anvil/stirrup, or oval window)

Deafness cont. . .

Sensorineural (Nerve) Deafness: occurs when the hair cells are damaged (usually by loud noises). “Ringing in your ears” often sign of damaged hair cells. Once cells are destroyed, they remain dead. More common type of deafness – occurs gradually over time

OTHER SENSES

Touch• When skin is indented, pierced, or experiencing change in

temperature, the sense of touch is activated.• 4 sensations – pressure, temperature, texture, pain

• 1. some nerve endings respond to pressure, others to temperature.

• 2. Brain interprets intensity and placement• 3. Nerve endings more concentrated in some body parts

(fingertips = higher nerve concentration & more sensitive; elbow = fewer concentration and less sensitive) – lips, fingertips are most sensitive; torso is least sensitive

• 4. If touch and temperature receptors are stimulated sharply, a different nerve ending, pain receptors, fire.

Touch cont. . .

• Gate Control Theory: explains how we experience pain. Some pain messages have high priority. The higher the priority, the more the gate swings open, the more we feel pain – like a continuum– Temps below 41 degrees and above 113

degrees cause us to feel pain

Taste

• Chemical Sense. Chemicals from the foods we eat are absorbed by taste buds.

• 1. Taste buds located on papillae- visible bumps you see on tongue

• 2. Humans sense 4 types: sweet, salty, bitter and sour

Taste cont. . .

• 3. People differ in ability to taste: more densely packed buds = more chemical absorbed = more intense taste – super tasters

• 4. Flavor of food is actually a combo of taste and smell (ex: close eyes, hold nose and taste ability deceases . . . apple and raw potato . . . explains why it isn’t as enjoyable to eat when you have a cold and you’re stopped up.

Smell

• Also a chemical sense• 1. Molecules of substances rise in

the air, are drawn to your nose & settle in a mucous membrane at the top of each nostril and are absorbed by receptor cells located there. Receptor cells are linked to the olfactory bulb which sends info to the brain

Smell cont . . .

• 2. Nerve fibers from olfactory bulb connect to the brain at the amygdale and hippocampus, the limbic system (responsible for emotional impulses and memory)

• Smell doesn’t go through the thalamus like all the other senses. This may explain why smell triggers strong memories and feelings

Smell cont . . .

• 3. Animals have many more olfactory receptors (dogs, sharks, etc.)

• They can smell prey long before they can see it.

• 4. Women typically have a stronger sense of smell (connected to estrogen)

Body Position Senses

• 1. Vestibular Sense: tells about overall body orientation in space

• Three semicircular canals in the inner ear give brain feedback about body orientation.

• Canals = tubes partially filled with fluid: when head moves, fluid moves, hair cells move, activate neurons which fire to the brain

Body Positions Senses cont . . .

• 2. Kinesthetic Sense: feedback about position of specific body parts . – hand –eye or foot-eye coordination

• Receptors in muscles and joints send info to the brain about limbs.

PERCEPTION

Figure Ground Relationship

• Our brain designates what the main figure is and what the background is. We may perceive different images from each other based on this designation

Gestalt Rules of Perception

• Gestalt psychologists study rules of perception. We perceive images as groups – we see the whole picture, not individual details– 1.) Proximity – objects close together perceived

holistically– 2.) Similarity – objects similar in appearance

perceived together– 3.) Continuity – objects that form a continuous trail

are perceived together– 4.) Closure – we mentally close in boundaries to

perceive a recognizable image

Proximity

Closure

Similarity

Continuity

Monocular Depth Cues Monocular Cues require one eye; tricks an artist uses to make a 2-D surface appear 3-d

1.) Linear Perspective

Monocular Depth Cues

2.) Relative Size 3.) interposition

Monocular Depth Cues

4.) texture gradient 5.) shadowing

What cues to you see….

Binocular Depth Cues

• Require both eyes – our ability to perceive depth in the real world– 1.) Binocular/retinal disparity: each eye sees

an object from a slightly different angle. Brain gets the L and R image. The further away an object is, the less disparity between the L and R image. Closer images have greater disparity

– 2.) Convergence: as objects get closer to our face, the eyes converge to stay focused

CULTURE

• Culture also affects our perceptions