Perception exam 1

What is the distal stimulus, proximal stimulus and the percept?

• Distal stimulus = real object, 

• proximal stimulus = retinal/projected image (flipped), 

• percept = perceived image in mind’s eye (right way up again)

Diagram and describe 7 parts of the eye.

Retina = layer of receptor cells (rods and cones) that receive light and turn it into (transduce) neural impulses

Pupil = small hole created by the iris that expands and contracts to let more or less light into the eye

Lens = small clear disc behind the pupil that expands and contracts (accommodates) to focus on the image

Optic Nerve = the neural pathway that connects the eye to the brain, receives signals from receptors

Iris = Muscles that contract to make the pupil bigger or smaller

Cornea = outer layer of the eye, bends light to help focus vision, protects eye from damage.

Vitreous Humor = yellow tinted liquid that helps the eye maintain its shape

What is the electromagnetic spectrum? What parts of the spectrum are we sensitive to and why?

• Spectrum of all wavelengths

• Includes: Gamma rays, X-rays, UV, Visible Light, Infrared, Radar, FM, TV, Shortwave, and AM

• Humans are only sensitive to Visible Light

• We see visible light for evolutionary reasons, necessary for our survival

  • Red: blood 

  • Green: plants to eat

  • Blue: poisonous 

• Bees can see ultraviolet light which helps with pollination due to its presence on flowers.

What is the blind spot and what do we normally see in the blind spot?

• Optic nerve meets the retina

• No rods or cones

• Don't receive info from light that hits that area, but brain fills in missing information from the background.

What are rods and cones? What are their differences? How can the neural wiring that underlies each system explain their differences?

• Rods and cones are photoreceptors - translate light waves into information the brain can unsderstand

• Rods work better in dark lighting, while cones are able to interpret color and detail.

• Rods are overall more common in retinal layer, mostly in periphery, while most cones are in the fovea

• Rods have high sensitivity but low acuity

• Cones have low sensitivity but high acuity

• Rods = multiple to one ganglion cell - resulting in a lower threshold for activation

• Cones = one to one ganglion cell - preserves differences, resulting in higher detail of information sent to the brain

What is the distribution of rods and cones across the retina?

• Overall, there are more rods than cones in the retina.

• Rods are primarily in the periphery, with very few cones in this area.

• However, at the fovea (where the focus of vision is located, 0deg) the amount of rods dramatically decreases, and the amount of cones significantly increases.

• There are no rods nor cones in the blindspot, where the optic nerve joins the retina (14-19deg).

What is the importance of change at the receptor level?

• Receptors detect change in input

• Receptors receiving constant stimulation will adapt and stop responding to it.

• Change over time (temporal) and space (spatial) is important for receptors to function

• Demonstrated with stabilized retinal image.

What is a stabilized retinal image and how is it produced? (5 methods including the low tech and high tech methods).

• Light hits retina in same place - constant stimulation

• Low Tech

• High Tech

• Red splotch on green background

• Ping-Pong ball method (Ganzfeld)

• Paralyzing Agent

Stabilized retinal image: Low-tech

• Contact lens is applied with a vacuum, and an image is projected onto the contact lens

• Image moves along with microtremors and eye movements

• results in image disappearing due to lack of change at the receptor level

Stabilized retinal image: High-tech

• Tracking eye movement with a computer to synchronize moving image with microtremors

• Removes change at receptor level so results in participant being unable to see the image. 

Stabilized retinal image: Half ping Pong ball

• Ganzfeld

• Homogenous field of blank color (eg. cut an orange pingpong ball in half and hold it up to eye)

• Color will turn grey after receptors adapt 

Stabilized retinal image: Paralyzing agent

• Paralyzes eye muscles to prevent natural microtremors of the eye

• Results in visual grey fog due to lack of crossing edges

• Must be in a constrained headrest to avoid headmovement creating differences 

Stabilized retinal image: Red splotch on green background

• A colored background with a splotch of a different color that does not have defined edges (gradual blend out to background color)

• Focus eyes on dot on background color, and colored splotch will disappear

What are examples of stabilized-like effects from the other senses?

• Smell: Adapting to gas leak in house 

• Touch: Wearing jewellery every day, stop feeling that it’s there until you take it off

• Hearing: tuning out the sound of airplanes flying overhead frequently - notice it at someone else's house but they don't notice

• Taste: getting used to spicy foods the more you eat them

Describe Hubel and Wiesel’s feature detection theory. Describe a criticism of the theory.

Hubel and Wiesel used single-cell recordings (electrode inside of or next to a specific neuron) in cats and monkeys to measure individual neurons’ responses to various stimuli projected onto a blackboard. They found that neurons only respond to changes in stimulus at a specific orientation unique to each neuron, inside of the neuron’s receptive field. For example, one neuron may only fire if the change in stimulus is vertical, while another may only fire if the stimulus moves horizontally.

Describe a split brain study and what it tells us about the visual pathways.

• Surgical separation of the two hemispheres of the brain by cutting the corpus callosum

• (usually a last resort in patients with severe seizures)

• Results in a loss of communication between the two hemispheres

• If a word is presented only to the left visual field, split brain patients are not able to verbally identify what they have seen, but could identify it through pointing (though only with their left arm).

• This is because language processing occurs in the left hemisphere, which has not seen the word because the left visual field is connected to the right hemisphere, but as the right hemisphere controls the left side of the body, the patient can identify the word with the left arm.

Diagram the visual pathways from the retina to the visual cortex.

Retina → Optic nerve → LGN → Visual cortex

Describe the LGN and its layers.

• LGN - Lateral Geniculate Nucleus

• Six layers, right side + left side

• 2, 3, and 5 receive input from same side eye (ipsilateral)

  • Layer 2/3/5 right lgn receives input from right eye (right retina, receiving info from object in left visual field), 

  • layer 2/3/5 left lgn receives input from the left eye (left retina, receiving info from object in right visual field)

• 1, 4 and 6 receive input from the opposite eye (contralateral)

  • Layer 1/4/6 right lgn receives input from left eye (right retina, receiving info from object in left visual field), 

  • layer 1/4/6 left lgn receives input from the right eye (left retina, receiving info from object in right visual field)

• 1 & 2 = interpret movement (magnocellular) 

• 3, 4, 5, and 6 = interpret color and texture (Parvocellular)

What did Schiller do and what did he find?

• Systematic injection of neurotoxins to lesion individual LGN layers on Rhesus Monkey. 

• Trained monkey to press buttons to identify the object they saw

• Discovered the abilities of each layer (1&2 movement; 3, 4, 5, & 6 color and texture) as the monkeys would not be able to identify this function of the object when that layer was lesioned

Describe the Gauthier et al “greebles study”(1999) study and the fusiform face area and what these tells us about the visual system.

• Used fMRI to investigate brain activity in response to “greebles” (unfamiliar(novel) bird like 3d objects) before and after becoming an expert in them. 

• Fusiform face area began with high activity levels in response to faces, but no activity in response to a greeble

• After just four days of experience with greebles, the fusiform face area was more active when the participant was presented with a greeble, and also reduced in activity in response to faces. 

• Tells us that the fusiform face area may be used to recognize not just faces, but familiar objects that are relevant. 

• Also demonstrates (functional) brain plasticity and how areas of the brain can adapt and change.

What is figure-ground segregation and what are some of the rules that govern the process?

• Visual system can separate an object from the background

  • Attention: shifting focus between the object and background can change the percept

  • Symmetry: symmetrical shapes are more likely to be perceived as figures than backgrounds

  • Internal priming: past experience and expectations can influence perception, if you have previously been thinking about an object then you are more likely to see it as a figure. (eg. dalmatian b&w illusion)

  • Motion: moving elements are more likely to be perceived as the figure

What is shape from shading? What does it tell us about our visual system?

Perception is influenced by assumptions about where the light is coming from, we usually assume light comes from above. We use information from the shading of an object to determine its shape.

What is size constancy? Equivalent Stimuli?

• Size constancy = perceived size stays the same despite change in retinal image

• Equivalent stimuli = same retinal image from different stimuli

What is the relationship between size and distance?

• Perceived size depends on perceived distance

• percept-percept coupling (distance percept influences size percept)

• Demonstrated by Lightbulb experiment: 

  • Staring at a lightbulb for an extended period of time to create a afterimage that stays on the retina, look at this afterimage projected onto the whiteboard (further) compared to on your hand (closer), changes the perceived distance of the afterimage, which makes the afterimage appear larger on the board and smaller on your hand 

  • Even though retinal image did not change, perceived distance did, which made perceived size also change

Describe in detail the Holway and Boring (1941) study on size perception. What was done and what was found. Include a detailed graph of the results and a diagram of the laboratory arrangements. Why do you think the data for condition 4 are not flat? How would you test your idea?

• Method: perpendicular hallway, with differently sized test circles at increasing distances so that they project the same retinal image (equivalent stimuli). 

• Participants adjusted the size of a comparison circle (located to their right) to the perceived size of each of the test circles.

• Did this for four conditions to systematically remove distance cues

  • 1. normal vision

  • 2. One eye closed, removing binocular disparity

  • 3. One eye closed + looking through a pinhole - removing binocular disparity and accommodation of the lens

  • 4. One eye closed + looking through a pinhole + in dim lighting (nothing apart from test circles visible)- removing binocular disparity and accommodation of the lens and pictorial cues

• Tested the relationship between distance cues, perceived distance, and perceived size

• Findings:

  • Condition 1 (normal vision) actually overestimated size of test circles

  • Condition 2 (one eye) was closest to the real size of the circles, but slightly underestimated

  • Condition 3 (pinhole) was a bigger underestimation, and condition 4 (no pictorial cues) was even less accurate

  • However, condition 4 did not reflect the visual angle, showing there was still some awareness of increase in size (increase in perceived distance), which may have been due to a flaw in the study’s design - participants still had the motion parallax cue when moving their vision from the test circles to the comparison circle.

• To remove this variable, I would be sure to have the comparison circle as close as possible to the test circles, and maybe also have the test circles be made of LED panels and turned off before the participant can move their visual focus to the comparison circle.

What is the moon illusion? What was Boring explanation? Rock’s?

• Moon looks bigger on the horizon than at the zenith

• Boring: eye elevation hypothesis - looking up stretches/contorts the eye shape and distorts the retinal image to be smaller

• Rock & Kauffman criticism of boring: the reverse effect was not seen with participants laying on their back and straight at zenith and looking up for horizon (with boring you would expect zenith to now look bigger but it still looked smaller)

• Rock: apparent distance theory - perceived distance to horizon is further than perceived distance to zenith, related to aristotle crystal bowl theory/vault of the heavens. 

• Criticism of rock: people introspectively consider the zenith to be further than the horizon

• Rock’s comeback: The illusion has nothing to do with conscious perception, more to do with the visual system (hardware?)

What evidence is there that experience can affect the Muller-Lyer illusion?

• Gregory cross cultural study

• Carpentered environment hypothesis - cross cultural study on people who were raised in round houses

• Experience with square angles primes us to perceive lines as corners of room

• Warps the perceived distance, in turn affects perceived size

Describe Ivo Kohler’s study using inverting goggles. What did he do and what did he find? What do his findings say about perception the brain?

• Goggles that flipped the distal stimulus (saw the world upside down), resulting in the proximal stimulus being in accordance with reality.  Percept was therefore flipped upside down compared to reality.

•  but After 2 weeks interacting with the environment, his percept adapted and became aligned with the proximal stimulus and the real world. 

• After removing the goggles, the effect was reversed, with the distal stimulus now the correct way and the proximal stimulus back to being upside down, but the percept was still upside down, went back to normal after x time.

• It shows perceptual plasticity, that perception is adaptable/flexible over time, but that it requires active interaction with the environment.

Describe Gibson’s Ecological approach to perception. Use the terms: texture element, higher order variable. Why is it considered a “ground” approach? How does it explain size perception?

• Textures common in environment, especially on the ground

• Determines size based on ratio (higher order variable) in respect to texture elements

MRI

• Magnetic resonance imaging

• Uses strong magnetic field in a cylinder scanner to align hydrogen atoms

• Produces detailed image of brain structure

fMRI

• Functional magnetic resonance imaging

• Tracks oxygenated blood flow in brain in response to a stimulus

• Higher blood flow = more brain activity

• Observes changes over time

PET

• Positron emission tomography

• Radioactive glucose injected into blood

• radioactivity is detected in higher amounts in areas of the brain that are more active (using up more of the glucose)

EEG

• Electroencephalography

• Lots of electrodes are placed on scalp and measure electrical signals from the brain 

• High temporal resolution (can tell differences in activity over time)

ERP

• Event-related potential (functional EEG)

• Derived from EEG data (electrode cap), measures response to stimuli

• Links specific stimuli to specific neural responses

(f)NIS

• Near infrared spectroscopy

• Sensors that detect changes in temperature 

• Higher temperatures result from higher blood flow due to higher brain activity

• fNIS - functional, changes in response to a stimulus

TMS

• Transcranial magnetic stimulation 

• Magnetic field applied to external head, temporarily disrupts neural activity and disables(lesions) specific area of the brain 

• Can suppress of visual functioning 

CT (not on study guide)

• Computed tomography

• Effectively a 3d x-ray, builds a 3d image of the structure of the brain

Oculomotor Cues

• information that comes from how much we move the eye muscles/lens, 

  • Eg. accommodation of the lens → lens changes shape to focus, helps us determine focal distance

  • Eg. convergence → objects closer to the face (centered) will require they eyes to turn inwards more to look at it than objects further away

Movement Produced Cues

• information from the way objects behave when moving across your visual field (or as your visual field moves across them)

  • Eg. Motion parallax → closer objects move faster across your visual field than further objects.

  • Eg. Deletion and Accretion → the speed at which things disappear or reappear behind other objects tells us their relative distance. The closer the object, the faster deletion and accretion will occur

Monocular/Pictorial Cues

• information that comes from a 2d image (still work with one eye)

  • Eg. relative height → objects higher in the visual field are perceived as further away

  • Eg. occlusion → if one object covers another, the covered object is perceived as further away

  • Eg. atmospheric perspective → objects further away will be less defined and less saturated, due to density of the atmosphere filtering the light

  • Eg. Perspective convergence → parallel lines appear to converge as they get further away, assumption of depth 

Binocular cues

• cues that require two eyes

• Eg. Binocular Disparity → information from the difference between the two images received by the left vs right eye. The closer the object, the greater difference between the two images