The Stroop Effect (1)

RedBlueGreenBlackGreenBlue

The Stroop Effect (2)

GreenRedBlueBlackBlueRed

Definitions

• Sensation:The process of stimulating receptors

• Perception:Interpretation & selection of sensory input

The Retina

Made of about 107 million transducers:

100 million rods

7 million cones

Rods

• Mostly in the periphery• More light sensitive• Detect light and dark• Insensitive to red• Take 20-30 minutes to fully adapt to darkness

Cones

• Mostly in the fovea• Less light sensitive• Detect colors• Have best detail vision• Adapt fully to darkness in 2-3 minutes

The Young-Helmholtz trichromatic theory:

The Opponent Process Theory

Cells are connected so as to place sensations of:

• red in opposition to green

• blue in opposition to yellow

• black in opposition to white

Color Vision

• The trichromatic theory explains perception at the receptor level

• The opponent process theory explains it at higher brain levels

Seeing Afterimages

In the following slide, fix your eyeson the dot in the center of the flag

Lateral Inhibition

• Cells in the retina are connected laterally by amacrine cells

• Works to enhance contrasts

Lateral InhibitionSee the glowing white spots where the black lines cross?

Ear Structures

Ear Structures

• Pinna: The external ear. Amplifies sound. Funnels energy to the middle ear. • Typanic Membrane (eardrum): Moves in response to sound waves. Converts sound

energy to mechanical energy .• Ossicles: The hammer (maleus), anvil (incus), & stirrup (stapes). Transmit & amplify

motion of eardrum

Ear Structures

• Cochlea: A fluid-filled chamber. Hair cells are attached to the basilar membrane . Converts mechanical energy to neural impulses.

• Bone Conduction: Sound is also transmitted to the cochlea through contact with skull bones. This is why your voice sounds odd in recordings

Hearing

Sound Attributes• Pitch: determined by frequency • Loudness: determined by amplitude• Timbre: Complexity of the sound (number of component waves involved in it)

Sound Waves

Hearing Loss

Hair cells, once lost, do not regenerateEven some children's toys can cause permanent hearing loss

Hearing Loss

Usually caused by continuous exposure to excessive noise The louder the noise, the less exposure needed

Chemical Senses

• Consist of smell & taste

• Evoke memories, emotions

• Humans vary greatly in chemical sensitivity

Olfaction (Smell)

• Senses vaporized molecules

• Consists of 10 million rods embedded in the olfactory epithelium

Olfaction (Smell)

• Olfactory Bulbs: Matchstick-sized; Integrate signals from the olfactory rods, send them on to the brain

• Turbinate Bones: Filter out dust and warm incoming air. Protect the olfactory epithelium.

• Olfactory Rods: There are more than 100 different types. Each responds to different chemicals

Smell Sensitivity

• Sense of smell varies among animals

• Dogs have 200 million olfactory rods, spread out in a much bigger nose

• Humans differ greatly in ability to detect smells

• The most sensitive people are 20 times more sensitive than the least

Taste Buds

The least numerous sensory receptors(humans have only about 10,000)

Taste

• Involves only 4 sensations: Sweet, sour, salty, bitter

• Most of what we consider taste is actually smell

• Texture is very important in enjoyment of food

• People love fats for the smooth feeling they give food (most are tasteless)

Taste Changes

• There are no taste buds in the center of the tongue

• Taste buds constantly replaced (like olfactory rods)

• Taste sensitivity changes very little with age

• Enjoyment of food among the aged is reduced by loss of sense of smell

Somasthetic Senses

• Kinesthetic sense: A moving sense

• Vestibular sense: Being oriented

• Touch: Feeling well

• Temperature

Skin Senses

• The largest sensory apparatus, involves heat, cold, pressure, pain

• Sensitivity varies throughout the body, reflected in the amount of brain devoted to each section of skin

• The hands & face predominate

Pain

• Important for survival • Motivates us to protect the body, tend injuries,

rest, seek medical help. • Gate Theory:

– Suggests an area in the spinal cord where fast-conducting nerve fibers can block the messages of small, slow conducting fibers.

– Suggests humans can block pain even when severely injured

– Explains why the badly injured may not even notice an injury

Endorphins

• Slow firing of pain neurons

• Accupuncture & placebos work through endorphin release

• "Runner's high" involves endorphin production

• Can be blocked by endorphin-blocking drugs

Body Senses

• Kinesthetic Sense– Knowledge of the position and motion of body parts.– Driven by receptors in muscles, joints, and ligaments

• Vestibular Sense– Involves the semicircular canals & the vestibular sacs – Senses acceleration, not uniform motion– Motion sickness arises when vision and the vestibular

sense give rise to different messages

Subliminal Persuasion

• Influence by messages that are below your level of awareness

Ex: taped messages that are below auditory level

• Double-blind studies have found little support for the efficacy of subliminal persuasion tapes (See the following example.)

Subliminal Persuasion

• Example:In one study, subjects were given audio tapes labeled for weight loss.• Half were given actual weight loss tapes• Half were given smoke-ending tapes

• Results:

The tapes with subliminal anti-smoking messages were just as effective as those with weight-loss messages.

The label mattered, not the messages.

Extra-Sensory Perception

• Telepathy: Detecting others' thoughts• Clairvoyance: Knowing things that can't be

sensed• Precognition: Predicting the future

– Psychology is concerned with evidence– Evidence of psychic ability under controlled conditions

is lacking

Consider this: If you could read minds, couldn't you find something more worthy (and profitable) for your

talent than to do cheap parlor tricks?

Definitions-Psychophysics

• Absolute Threshold:The point where you can tell the stimulus is

there vs. not there 50% of the time

• Difference Threshold:The smallest change in the stimulus that is just

detectable 50% of the time

Psychophysics: A World of Experience

• Detecting signals– Signal detection theory– Sensitivity– Bias

Intermediate Vision

• Perceptual organization– Figure– Ground

We organize the world so some parts of a stimulus appear to stand out (figure) in front of other parts (ground)

Figure-Ground

• The whole is greater than the sum of its parts.

• A group of sensory elements forms something new that is greater than itself

Gestalt Principles

Good ContinuationClosureSimplicity

Figure-GroundSimilarityProximity

Similarity

• We group things that are similar in color, shape, etc. into single units and see them as belonging together

• Note in the following example how similarity alters our perception of the stimulus as rows vs. columns of circles

Similarity

Repeat

Proximity

• We perceive as a unit things that are closer together relative to other things

• Note the tendency to see the next example as a set of columns first, then a set of rows, despite the fact the horizontal distance between circles doesn't change

Proximity

Repeat

Good Continuation

• We group things together if they appear to form a continuous pattern

Example: lines are continued through if they cross other lines

• In the next example, we see the stimulus as a wavy line crossing a straight line, although numerous other interpretations are possible.

Good Continuation

Repeat

Closure

We tend to complete figures with gaps in them, by ignoring the gaps and mentally filling in what we believe should be there

Good Continuation

Repeat

Simplicity

• We tend to impose the simplest, best-fitting interpretation on any stimulus.

• In the following picture, we tend to see overlapping simple geometric figures rather than complex polygons.

Good Continuation

Repeat

Depth Perception

• Cues can be monocular or binocular

• Some appear to be innate, whereas others appear to be learned

Binocular Cues

Convergence -- the lenses of your eyes move closer together when things are close, farther apart when things are farther away

Convergence

Repeat

Binocular Cues

Binocular Disparity -- • Each eye gets a different picture of the

world• The greater the difference between

the pictures, the closer the object

Monocular Cues

• Linear Perspective --parallel lines converge into the distance

• Relative Size -- bigger things appear to be closer

• Texture Gradient --textures become finer as things become

more distant.

Monocular Cues

• Shading -- Shadowing distinguishes bulges from indentationsLargely a learned cue

• Motion Parallax -- Objects closer than our fixation point move opposite to

our direction of motion. Objects farther away move in the same direction as us.

Monocular Cues

• Overlap or Interposition --–Closer objects overlap objects that are

farther away

Relative SizeLinear Perspective

Monocular Cues

Overlap

Visual Illusions

• Reveal information about the visual system

• Sometimes derive from perspective cues

The Bending Lines Illusion

Repeat

Illusions

Repeat

Depth Cues

Ambiguous Images

• Have 2 interpretations, can be switched at will

• Demonstrate the existence of top-down processing

The Schroeder Staircase

Impossible Images

• Changing perspective gradually in a large picture can create impossible figures (as in some Escher prints).

• If the figure is large enough, you cannot perceive it all at once, so the change in perspective is not readily apparent.

• Contrast the relative ambiguity of the large and small figures on the next slide.

2 Tongs/ 3 Tongs

Another Impossible Figure

Late Vision

• Knowing more than you can see

• Informed perception– Perceptual expectancies