PSYC 1200 Ch.5: Sensation and Perception

Sensation

The detection, by sensory organs, of physical energy emitted or reflected by physical objects (physical stimuli)

Where does sensation begin at?

Sense receptors

Sense receptors

Specialized cells needed to sense different stimuli and sends messages to sensory neurons

Perception

The process by which the brain organizes and interprets sensory information

Anatomical code

The principle that different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain

What do we use to see and hear? (trick question)

Brain, not our eyes and ears

Synesthesia

A condition in which a sensation in one modality consistently evokes a sensation in another

What condition is smelling colours an example of?

Synesthesia

Possible cause of synesthesia

Increased neural connections or a lack of inhibition between sensory areas in the brain

What does anatomical encoding not explain?

Why our sense are separate or the variations of experience within a particular sense

Functional code includes what information? (4)

• Which cells are firing

• How many cells are firing

• Rate at which cells are firing

• Patter of each cell’s firing

Stimulus thresholds (2)

1. Absolute threshold

2. Difference threshold

Absolute threshold

The minimum amount of energy or quantity of a stimulus required for it to be reliable detected at least 50% of the time it is presented

Difference threshold

Smallest difference between two stimuli that a subject can detect

“just noticeable difference” fraction name

Weber fraction

Does the Weber’s fraction stay consistent or change?

Stay consistent

What does the Weber’s fraction tell us as the physical stimuli gets stronger?

As the magnitude of the stimuli increases the larger the difference has to be to be able to detect it

Signal detection theory

A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process

Signal detections (4)

1. Hit: Stimuli is present; stimuli perceived

2. Miss: Stimuli is present; stimuli not perceived

3. False Alarm: Stimuli is not present; perceive as if stimuli was present

4. Correct rejection: Stimuli is not present; perceive as stimuli not present

Sensory adaptation

Decline in sensory responsiveness when a stimulus is unchanging or repetitious

Is sensory adaption beneficial? If not, give an example why.

Usually beneficial

At times not - e.g. smell of smoke in the house

Do we adapt to all stimulus?

No, we never completely adapt to very intense stimuli

Is too little sensory stimulation bad?

Depends on personal factors and how people perceive it as their own

Selective attention

Process of focusing on selected aspects of the environment while blocking out others

Inattentional blindness

Failure to consciously perceive something you are looking at because you are not attending to it

What is the stimulus for vision and what is its form?

light - form of electromagnetic radiation

3 dimensions of visual experience

1. Hue

2. Saturation

3. Brightness

Hue

The dimension of visual experience specified by color names, is related to the wavelength of light

Short and long wavelength hue (colour)

Short - blue/violet

Long - red/orange

Saturation (colourfulness)

The dimension of visual experience related to the complexity of light - how wide or narrow the range of wavelength is

Colours in white

All colours

Saturation of black

No saturation at all - void

Brightness

The amount, or intensity, of the light an object emits or reflects and corresponds to the amplitude (maximum height) of the light wave

Parts of the eye (6)

1. Sclera

2. Cornea

3. Pupil

4. Iris

5. Lens

6. Retina (cones and rods)

Sclera

White outer layer of eye

Cornea (3)

Clear layer that covers the front of the eye; protects the high and bends light

Pupil

Regulates amount of light let into the eye

Iris

Round muscle that adjusts the size of the pupil

Lens (2)

Clear structure that focuses light onto the back of the eye; changes shape of light

Retina

Neural tissue lining the back of the eyeballs interior that contain the receptors for vision (cones and rods)

Cones

Produce high-detail, colour vision at our point of visual focus; concentrated on fovea (small pit in the center of retina)

Rods

Provide peripheral vision and are specialized for low light conditions; located on outer regions of the retina

Phototransduction

The process by which rods and cones gain sensitivity to low light levels

How are visuals perceived in the eye and brain?

Eye sees visuals upside down but the brain flips it back right side up

Cells involved in light to nerve

1. Bipolar neurons

2. Ganglion cells

3. Optic discs

4. Optic nerves

Bipolar neurons

Synapse onto photoreceptors and carry message to ganglion cells

Ganglion cells

Transmits signals from bipolar neurons to the brain

Optic disc (how blind spots are created)

Area on retina lacking rods and cones due to the optic nerve in the way - creating a blind spot

Optic nerve

Axon tracts from ganglion cells leading to the brain

Feature-detector cells in the visual areas of the brain detect what?

Specific aspects of the visual world, such as lines at various orientations

What parts of the brain have feature-detection cells and what do they perceive? (3)

• Above the cerebellum - faces

• Hippocampus - environment

• Occipital cortex - body parts

Trichromatic Theory (Young-Helmholtz Theory)

Colour vision is determined by three different cone types that are sensitive to short, medium, and long wavelength light (blue, green, red)

Combined activity of all three cone types generate what in the Trichromatic Theory?

A unique signature associated with each perceived colour, even colours without a corresponding wavelength

What cone distribution is depicted by these pictures?

Left - trichromat cone distribution (normal)

Right - dichromat cone distribution

What type of trait is dichromatic (lack red cones)?

Recessive x-linked trait

Opponent-process theory (and colours)

Perceive colour in terms of opposite ends of the spectrum (red to green, yellow to blue, white to black)

Oppose-process cells

In the retina and thalamus; respond in opposite fashion to short and long wavelengths of light

How do opponent-process theory work?

Opponent-process cells that are inhibited (red cells) by a particular colour (green cells) produce a burst of firing when the color is removed (red cells on white screen)

Opponent-process theory explains why we are susceptible to what?

Negative afterimages - seeing red after staring at green

Gestalt psychologists

First to study how people organize the world visually into:

• meaningful units

• patterns

Gestalt principles

Describe strategies used by the visual system to group sensory building blocks into perceptual units

Types of Gestalt principles (4)

• Figure and Ground

• Proximity and Similarity

• Continuity

• Closure

Figure and Ground idea

Objects or “figures” in our environment tend to stand out against a background

Proximity and Similarity

Ways we group things together

Continuity

Perceptual rule that lines and other objects tend to be continuous, rather than abruptly changing direction

Closure

People tend to fill in blanks to perceive a complete object whenever an external stimuli partially matches the object

Visual pathways (2)

1. Dorsal stream

2. Ventral stream

Dorsal stream

• Where/how

• Guides interaction with objects

• Responsible for depth and motion perception

Where is the dorsal stream located

Extends from visual cortex to the parietal lobe

Binocular depth cues

Distance cues that are based on the differing perspective of both eyes

Types of binocular depth cues (2)

• Convergence

• Retinal disparity

Convergence

Depth cue; when the eye muscles contract so that both eyes focus on a single object

Retinal disparity

Depth cue; the difference in perspective provided by each eye

Stereopsis

Sense of depth

When do we use binocular and monocular cues in terms of distance?

Binocular - 50 feet or less

Monocular - anthing farther

Monocular depth cues

Depth cues that depend on only one eye

Types of monocular depth cues (7)

• Interposition

• Linear perspective

• Motion parallax

• Relative size

• Relative clarity

• Texture gradients

• Light and shadow

Interposition

When an object is interposed between the viewer and a second object, partly blocking the view of the second object, the first object is perceived as being closer

Linear perspective

When two lines known to be parallel appear to be coming together or converging, they imply the existence of depth

Motion Parallax

When an observer is moving, objects appear to move at different speeds and in different directions.

Closer an object - faster it seems to move and seem to move backward

Farther an object - slower it seems to move and seem to move forward

Relative size

Perceive the same object but a smaller size as being farther

Relative clarity

Closer objects seem to have more detail as farther objects seem more blurry and gradient

Texture gradients

Able to see green, larger, details in closer objects, but only see a field of yellow when looking farther

Light and shadow

Allow us to understand 3D objects and its relative distance

Ventral stream (6)

• ‘What’

• Responsible for object and face recognition

• Fusiform face area

• Pareidolia

• Prosopagnosia

• Perception Constancies

Where is the ventral stream located

Extends from the visual cortex to the temporal lobe

Pareidolia

Seeing faces in non-face objects

Prosopagnosia

No ability to recognize faces

Fusiform face area is responsible for what and not specific to what?

Visual expertise, not specific to faces

Perceptual constancies

The accurate perception of objects as stable or unchanged despite changes in sensory patterns they might produce

Best-studied visual perceptual constancies (5)

• Size

• Shape

• Location

• Brightness

• Color

Size constancy example

Shape constancy example

Heavily context dependent - need to understand how the object works first

Location constancy example

Tendency for objects to appear stable in their positions even when the observer moves (car door)

Brightness constancy example

Perceptual illusions

When sensory cues are misleading or when we misinterpret cues