2 perception basics

Question 1

What is the difference between sensation and perception?

Answer 1

Sensation refers to the detection of stimuli by sensory organs, while

perception involves the recognition and interpretation of sensory information.

Question 2

What is the perceptual process roughly?

Answer 2

Detection
A stimulus (e.g., light, sound, chemicals) is detected in the environment.

Transduction
The stimulus is converted into nerve impulses by sensory organs.

Neural Pathway
Nerve impulses travel along afferent pathways to the brain, often through the thalamus to sensory areas of the cerebral
cortex.

Interpretation
The brain interprets these signals as subjective experiences, leading to perception.

Question 3

How do visual illusions demonstrate stimuli interpretation?

Answer 3

Dale Purves suggests that the visual system evolved to enable successful behavior in the world, not necessarily to provide a perfect
photographic reality

The visual system must process two-dimensional images on the retina and infer three-dimensional properties of the world.

The brain interprets ambiguous stimuli, using probabilistic inferences about the environment to guide perception.

-> align with evolutionary development

Question 4

What is bottom-up visual processing?

Answer 4

Data-Driven Approach
Perception begins with the input of sensory
information from the environment.
Feature Detection
The visual system detects basic features like
edges, colors, and shapes from the visual stimuli.
Building Complexity
These basic features are gradually combined to form more complex perceptions (e.g., recognizing objects).
No Prior Knowledge
Relies purely on sensory input without the
influence of prior knowledge or expectations.

Question 5

What is top-down visual processing?

Answer 5

Concept-Driven Approach
Perception is guided by prior knowledge, experiences, and expectations.
Hypothesis Testing
The brain uses existing cognitive frameworks to interpret and predict sensory information.
Influence on Perception
Expectations can shape or alter the perception of visual stimuli, leading to faster recognition or potential errors.
Contextual Influence
Perception is influenced by the context in which the stimulus is encountered.

perceiving objects and people
top-down (do you know them, do you like them)
context matters
hearing words in a sentence
language comprehension
speech segmentation (top-down)
experiencing pain
pain occurs when receptors on the skin, nociceptors, are stimulated
adrenaline, will, motivation
attention, distractions, expectations (top-down)

Question 6

How does visual perception work in the eye?

Answer 6

eye - major sensory organ
cornea - transparent covering the eye
pupil - small opening in the eye through which light passes
iris - colored portion of the eye after passing through the pupil, light crosses the lens
lens = transparent structure that provides additional focus

Light enters the eye:
Light reflects off objects and enters the eye through the cornea.
Cornea:
The cornea refracts (bends) the light towards the pupil.
Pupil:
The pupil regulates the amount of light that enters the eye and is controlled by the iris.

Lens:
Light passes through the lens, which further focuses it onto the retina by changing shape (accommodation).

Question 7

How does phototransduction work then at the back of the eye?

Answer 7

Retina:
The retina contains photoreceptors (rods and cones) that convert light into neural signals.
Rods are responsible for vision in low light.
Cones detect color and fine detail.

Phototransduction:
Photoreceptors initiate a chemical reaction that converts light into electrical signals.
Bipolar cells:
Electrical signals from photoreceptors are transmitted to bipolar cells in the retina.
Ganglion cells:
Bipolar cells transmit signals to ganglion cells, which collect visual information

Question 8

How is visual information then futher processed in the brain?

Answer 8

Optic nerve:
Ganglion cell axons bundle together to form the optic nerve, which carries visual information to the brain.

Optic chiasm:
At the optic chiasm, nerve fibers from the nasal (inner) half of each retina cross to the opposite side, while those from the temporal (outer) half remain on the same side.

Optic tracts:
After the optic chiasm, the fibers form the optic tracts, which carry information to the brain’s lateral geniculate nucleus LGN.

Lateral geniculate nucleus LGN
Located in the thalamus, the LGN processes and relays visual information to the visual cortex.

Optic radiations:
Signals from the LGN are sent through the optic radiations to the primary visual cortex V1 in the occipital lobe.
Primary visual cortex V1
The primary visual cortex processes basic visual information such as edge detection, orientation, and motion.
Higher visual areas:
From V1, information is distributed to higher visual areas including:
V2, V3 Further process shape, color, and motion.
V4 Specializes in color and form processing.
MT/V5 Processes motion

Question 9

What do the ventral and dorsal pathway process?

Answer 9

ventral pathway - “what pathwayˮ
object recognition and identification
dorsal pathway - “where/how pathwayˮ
location in space and interaction with stimulus

Question 10

What is the Young-Helmholtz trichromatic theory of color vision?

Answer 10

Color vision is mediated by three types of cones in the retina.

Cone Sensitivity: Each type of cone is sensitive to a specific range of wavelengths—short (blue), medium (green), and long (red).

Color Perception: Colors are perceived by the brain based on the combined stimulation of these three types of cones.

Color Matching: Helmholtz demonstrated that any color could be matched by combining three different wavelengths of light, supporting the theory.

Visual Spectrum: The three types of cones allow the perception of millions of colors within the visible spectrum.

Question 11

What is photopic versus scotopic vision?

Answer 11

-Photopic Vision
- Occurs in bright light conditions.
- Mediated by cones in the retina.
- Provides high-resolution, color vision.
- Dominates during daytime or well-lit environments.

Scotopic Vision
- Occurs in low light conditions.
- Mediated by rods in the retina.
- Provides vision in shades of gray, without color.
- Dominates during nighttime or dim environments.

Question 12

What is the opponent process theory?

Answer 12

Basic Concept: Color vision is controlled by three opposing pairs of receptors.
Receptor Pairs: The pairs are red-green, blue-yellow, and black-white.

Opposition Mechanism: Activation of one color in a pair inhibits the perception of the opposing color.

Color Perception: The brain cannot perceive both colors in a pair simultaneously (e.g., no reddish-green).

Afterimages: Prolonged exposure to one color leads to an afterimage in the opposing color due to receptor fatigue.

Complementary Colors: Explains phenomena like afterimages and the perception of certain color combinations.

Question 13

What are binocular and monocular cues in depth perception?

Answer 13

Binocular Cues: Require both eyes (e.g., binocular disparity).
Monocular Cues: Require one eye (e.g., linear perspective, texture gradient).

Question 14

What is binocular disparity?

Answer 14

The difference in the images on the retina of the two eyes

Question 15

What is motion parallax?

Answer 15

depending on distance, objectts appear to move at different speeds and directions

Question 16

What is blur?

Answer 16

Increases when objects are away from fixation point

Question 17

What is familiar size?

Answer 17

We know objects size, we can use it to estimate its distance

Question 18

What is linear perspective?

Answer 18

parallel lines pointing away converging, reducing in size with distance

Question 19

What is interposition?

Answer 19

where a nearer object hides part of a more distant one

Question 20

What is texture?

Answer 20

gradient in texture density with distance

Question 21

What is accomodation?

Answer 21

thickening of the lens when focuses on a close subject

Question 22

What is vergence?

Answer 22

Eyes turn inwards to focus on very close objects than those further away

Question 23

What is synesthesia?

Answer 23

blending-of-sensations phenomenon

Synesthesia is a condition where stimulation of one sensory pathway leads to involuntary experiences in another sensory pathway.

Individuals might see colors when they hear music or associate specific numbers with particular colors.

The senses become intertwined, creating automatic and consistent sensory experiences across different modalities.

Includes grapheme-color synesthesia (letters/numbers perceived as colors) and chromesthesia (sounds trigger the perception of colors).

Believed to result from increased connectivity between sensory regions of the brain.

Question 24

What is stereoblindness?

Answer 24

Unable to respond to binocular cues
-> inability to perceive depth

Often associated with conditions like strabismus (misalignment of the eyes) or amblyopia (“lazy eye”).

Question 25

What is the vestibulo-ocular reflex ?

Answer 25

The vestibulo-ocular reflex (VOR) is a reflex that stabilizes vision by coordinating eye movement with head movement.

When the head moves in one direction, the VOR causes the eyes to move in the opposite direction, allowing the gaze to remain fixed on a target.

The reflex is controlled by the vestibular system in the inner ear, which detects head motion and sends signals to the eye muscles.

Essential for maintaining clear vision during activities such as walking, running, or any movement that involves head motion.

Dysfunction of the VOR can lead to blurred vision or dizziness, particularly during movement.

Question 26

What are hue, brightness and saturation?

Answer 26

• Hue:
  
  • Refers to the distinct characteristic of a color that allows it to be classified as red, blue, green, etc.
  • Determined by the wavelength of light.
  • Represents the basic color family.
• Brightness:
  
  • Also known as value or lightness.
  • Refers to the intensity or amount of light emitted or reflected by a color.
  • Higher brightness means the color is closer to white; lower brightness means it’s closer to black.
• Saturation:
  
  • Also known as chroma or colorfulness.
  • Refers to the purity of a color, or how much gray is mixed with it.
  • High saturation means the color is vivid and intense, while low saturation makes the color appear more muted or washed out.

Question 27

What are the essential characteristics of colour receptors (as per the trichromatic theory of vision)?

Answer 27

pigments in the cones (opsins) have different levels of absorption of light
waves
S,M,L cones (short, medium, long wavelength cone receptors)
400 nm - 700 nm
7 main colours: ROY G BIV
red, orange, yellow, green, blue, indigo, violet
blue receptors are the most sensitive, red the least
theres a genetic mutation in women giving them four types of cones
tetrachromatic vision

Question 28

What is colour blindness?

Answer 28

genetic alteration of one or more cone pigments
typically red-green blindness

The four types of color vision include:
Monochromatic: 500 shades of gray
Dichromatic: 10,000 colors
Trichromatic: 1 million colors
Tetrachromatic: 100 million colors
⇒ color vision at the receptor level

Question 29

What is the modern view of complementary colour theory?

Answer 29

afterimage seems to be generated in the cortex, not the retina

does not seem that green cells are activated because red cells are inhibited

each receptor pairing registers complementary colors

When you were staring at the red image, your brain got used to the red and
suppressed the signals it was getting from red cells. When you the shifted
your gaze to the white paper, your brain saw less red light than before and
mentally “subtracted” red from what it is seeing.

Hurvich and Jamesonʼs 1957
dual process theory

initial mechanism for capturing spectral information occurs through light
absorption in three separate types of cone receptors, as in the trichromatic
theory

information subsequently supplies three ‘channelsʼ: an achromatic (light dark) channel, which receives non-spectrally opponent input from both the long-wavelength and medium-wavelength cones, and two chromatic channels (red-green and blue-yellow) which receive spectrally opponent inputs that determine the colour seen, similar to the opponent-process
theory

Question 30

What is protanomaly?

Answer 30

RED
Protanopes are more likely to confuse
Black with many shades of red
Dark brown with dark green, dark orange, dark red, dark
blue/purple and black
Some blues with some reds, purples and dark pinks
Mid-greens with some oranges

Question 31

What is deuteranomaly?

Answer 31

GREEN
Mid-reds with mid-greens
Blue-greens with grey and mid-pinks
Bright greens with yellows
Pale pinks with light grey/white
Mid-reds with mid-brown
Light blues with lilac

Question 32

What is tritanomaly?

Answer 32

BLUE
extremely rare
light blues with greys
dark purples with black
mid-greens with blues
oranges with reds

Question 33

What is dichromacy?

Answer 33

inherited colour blindess
largely similar to pro and deuter but these are more light dependent

Question 34

What is monochromacy?

Answer 34

no colour
greyscale

Question 35

What are some statistics about colour blindness?

Answer 35

8% of men and 0.5% of women have red/green colour vision deficiency

rise in whiter populations
scandinavia: 10-11% of men

mixed race genes - high cvd

1% deuteranopes, 1% protanopes, 1% protanomalous and 5% deuteranomalous

half of colour blind people will have a mild anomalous deficiency, the other 50% have moderate or severe anomalous conditions

Question 36

What is the theory that more weight is assigned to reliable cues?

Answer 36

cue combination

Triesch (2002)
observers in VR tracked an object (shape, colour, size)
two attributes were unreliable on each trial
observers attached increasing weight to the consistent cue

Atkins (2001)
if motion indicated a different depth, observers made increasing use
of texture cue and decreasing use of motion
whichever visual cue correlated with the haptic cue was preferred
and this preference increased with practice

hypothesis 1: less ambiguous cues are regarded as more reliable
(consistent information)
hypothesis 2: a cue is regarded as reliable if inferences based on it are
consistent with those based on other available cues

maximum likelihood estimation

Question 37

What are limitations of cue integration theory?

Answer 37

limitations to cue integration theory
typically there are no large conflicts between cues
unfamiliarity of laboratory settings
observers do not process independent cues before integrating the
information
what is ideal performance in this context

Question 38

What is the P pathway?

Answer 38

The parvocellular pathway: it is most sensitive to colour and to fine detail; most of its input comes from cones)

P pathway associates with ventral pathway or stream that proceeds to the
inferotemporal cortex

Question 39

What is the M pathway?

Answer 39

The magnocellular pathway: it is most sensitive to movement
information; most of its input comes from rods

M pathway associates with dorsal pathway or stream that proceeds to the
posterior parietal cortex

Question 40

What are the fusiform gyrus and IT important for?

Answer 40

Area IT - inferior temporal cortex recognizes objects
Damage leads to visual agnosia (impaired ability to recognize objects)

Area fusiform gyrus - (part of the IT that recognizes faces, Damage leads to Prosopagnosia (impaired ability to recognize faces)

Question 41

What is a receptive field?

Answer 41

Definition: A receptive field is the specific area of the sensory space (e.g., a region of the retina in the visual system) where a stimulus will elicit a response from a particular neuron.

In Vision: In the visual system, the receptive field refers to the area of the retina that, when stimulated by light, activates a particular retinal ganglion cell or neuron in the visual pathway.

Function: The size and shape of a receptive field can determine the type of visual information that a neuron processes, such as edges, contrast, or movement.

Question 42

What did Hubel and Wiesel´s experiments on the neural basis of visual perception find?

Answer 42

Orientation Selectivity: They found that certain neurons in the primary visual cortex (V1) respond specifically to edges or bars of light at particular orientations, meaning these neurons are “tuned” to detect specific angles.

Location Specificity: These neurons only fired when the stimulus (e.g., a line or edge) was in a specific location on the retina, indicating that each neuron had a precise receptive field.

Direction Selectivity: Some neurons were also found to be selective not just for the orientation of the line, but also for the direction of motion, firing only when the line moved in a particular direction.

Columnar Organization: They discovered that neurons with similar orientation preferences are organized into columns within the visual cortex, creating a systematic map that processes different aspects of visual stimuli.

Topographical Map: Their work showed that the visual cortex is organized as a topographical map of the visual field, with neighboring neurons responding to neighboring areas of the visual field