Psych 315

Daniel Kish: echolocation

blind, echolocation → contour, dimension, texture, density, proximity

Transduction

Converting sensory stimulus into neural impulses

Cornea

 Outermost layer of tissue that protects eyes; helps focus light onto the retina

Pupil

black part in the center of the iris that controls the amount of light entering the eye

Iris

the colored part, helps control the size of the pupil to let more or less light into the eye

Lens (visual accommodation)

 can change its shape to focus on objects at different distances (i.e. visual accommodation)

Lens visual accommodation for nearby objects 

muscles tighten and bulge the lens

Lens visual accommodation for distant objects 

muscles relax and flatten the lens

Retina (retinal image)

• light-sensitive layer of tissue located at the back of the eye.

• convert light into electrical signals that are sent to the brain for visual perception.

• Light is inverted on the retina

Fovea

• center of the retina 

• provides sharp, central vision 

Ganglion cells

• Have long tails 

• receive signals from photoreceptor cells (rods and cones) through bipolar cells.

• integrate information, generate electrical impulses, and send them along their axons, which form the optic nerve.

Bipolar cells

transmits visual information from the photoreceptor cells (rods and cones) to the ganglion cells

Photoreceptors

• specialized cells located in the retina of the eye that convert light into electrical signals that are sent to the brain (i.e. transduction)

• Rods and cones

Optic nerve (blind spot)

• Tails of the ganglion cell go up to brain, bundled together to form your optic nerve 

• Don’t really have a blind spot because 

1. Eyes are not static, they are moving 

2. Brains fill it in

Thalamus

 the final relay point for sensory information before it reaches the cerebral cortex

Lateral geniculate nucleus (LGN)

 a key thalamic relay center in the brain's visual system, processing and organizing visual information from the retina before sending it to the primary visual cortex

Visual cortex (occipital lobe)

• The visual cortex is a network of brain cells within the occipital lobe that specializes in visual processing

• Occipital: located at the back of the head

Parietal cortex

• Functions: spatial navigation, planning voluntary movements, attention, and integrating information from various senses

• Located in the upper posterior portion of the brain, above the occipital lobe and behind the frontal lobe

Temporal cortex

• part of the brain's temporal lobe

• Responsible for processing auditory information, comprehending language, memory formation, and processing emotions and visual stimuli like objects and faces

Rods

• periphery of the retina 

• very sensitive to light 

• color-blind 

• lower acuity 

Cones

• In the fovea 

• Less sensitive to light 

• Color sensitive 

• Higher acuity 

Mach Band Illusion

It exaggerates the contrast between edges of the slightly differing shades of gray, as soon as they contact one another

Lateral Inhibition

• Neighboring cells inhibit each other by lowering their firing rates

• Brighter stimuli lead to more stimulation → higher firing rates

• More stimulated cells can inhibit their neighbors more

Feature detection

• Visual processing is so highly effective bc:

• 1. Functional specialization: Cells are specialized in function, i.e., in what they respond to. They share the work.

  • Disadvantage: Vulnerable to losing specific functions (e.g., akinetopsia)

• 2. Parallel processing: Many different types of analyses happen at the same time

  • This speeds up processing and allows for mutual influences without imposing an order

Functional specialization: Receptive fields

Cells are specialized in their receptive fields.

• Single-cell recordings allow us to define a cell’s receptive field.

  • Example: Center-surround organization of receptive fields in edge detectors

Akinetopsia

Inability to process motion 

Parallel processing

Many different types of analyses happen at the same time

• speeds up processing and allows for mutual influences wihtout imposing an order

Where System: What is it?

Location of objects and guiding our responses

Where System: Pathway

Occipital-parietal pathway

Where System: If lesioned…

Problems reaching for seen objects

What System: What is it?

Identification of objects

What System: Pathway

Occipital-temporal pathway

What System: If lesioned…

Visual agnosia

What is the binding problem?

Bistable figures

Figures that you can have two interpretations of the same information

Examples of bistable figures

Figure ground

principle of perception where brain distinguishes between central object (the figure) from its surrounding context (the ground) 

Bottom up influence

incoming information about the world (stimulus-driven)

Top-down influence

stored knowledge used to alter how the world is processed 

Gestalt Principles

similarity, proximity, good continuation, closure, simplicity

Gestalt Principle: Similarity

Stimuli that are similar to each other tend to be grouped together

Gestalt Principle: Proximity

tend to group nearby figures together

Gestalt Principle: Good continuation

 We tend to perceive stimuli in smooth, continuous ways

Gestalt Principle: Closure

We tend to fill in gaps to create a complete, whole object

Gestalt Principle: Simplicity

We tend to interpret a form in the simplest way possible

Perceptual Constancy

Even though the sensory information we receive changes, the properties of an object appear as constant to us

Unconscious inference

automatic, involuntary process by which our brain uses past experiences and assumptions to interpret ambiguous sensory info and form a  complete perception of the world, filling in missing details and creating meaningful images from the 2-D patterns on our retinas 

• Perceptions are not direct readings of reality but are actively constructed through educated guesses by our unconscious mind 

Examples of Perceptual constancy

Size constancy and shape constancy

Size constancy example

we know the person is the same size despite visual stimuli (him being closer or farther depicted) making him smaller

Shape constancy example

We can tell both objects are doors despite their different shapes (one door is open and the angle looks different) 

Depth perception

 The ability to perceive things in 3D and accurately judge the distance and position of objects

Oculomotor cues

sensory info from eye muscles that contribute to depth perception

When are oculomotor cues effective?

At short viewing distances

What dimension is the retinal image in?

2D

What is accommodation?

muscles in your eye adjust the shape of the lens to bring objects into sharp focus

Convergence

As you look at a close object, your eyes turn inward to focus on it. The amount of inward turning (convergence) provides the brain with information about the object's distance.

Binocular cues (disparity)

• relies on input from both eyes, binocular disparity each eye sees a slightly different image and the brain fuses them 

  • Disparity is most effect for objects up to 6m away 

  • Things change more when it is closer

Monocular cues

Pictorial cues

Things that come from the picture itself

Pictorial cue: Interposition (overlap)

When one object partially blocks (overlaps) another, the blocked object is perceived as being farther away, and the blocking object is seen as closer 

Pictorial cue: Relative size

When two objects are known (or assumed) to be similar in actual size, the one that casts a smaller image on the retina is perceived as being farther away (if two objects -> same actual size, farther one away = less space on retina = looks smaller)

Pictorial cue: Linear perspective

parallel lines (like railroad tracks or roads) appear to converge as they recede into the distance, giving a sense of depth. 

• The more they converge, the farther away they seem

Pictorial cue: Texture gradient

Surfaces with detailed texture appear clearer and more distinct when they are close, but as the surface extends into the distance, the texture becomes denser, finer, and less distinct—signaling depth.

Motion cues

Motion parallax

phenomenon that closer objects appear to move faster than distant objects when observer is in motion creating an illusion of depth

Optic flow

apparent motion of objects and surfaces in a scene that results from the relative movement between an observer and the scene itself

Apperceptive Agnosia

object recognition is impaired because you can’t perceptually process it 

What can you not do when you have apperceptive agnosia?

can’t name, copy, match, or discriminate the object

How can someone with apperceptive agnosia sometimes recognize an object?

From making inferences based on the features

Associative agnosia

objects recognition becomes impaired because you can’t associate relevant knowledge about the object from memory 

What can and cannot someone with associative agnosia do?

Can: perceive, copy and match objects

Cannot: name objects, but can describe them 

Prosopagnosia

Inability to recognize familiar faces

Prior experience

We recognize objects more easily when we encounter them

Frequency Effect

The more I encounter the object, the easier it should be for me to detect the object (FREQUENTLY)

Recency Effect

• Objects that have been recently processed are better recognized 

• Recency effect is larger on low frequency items

Bottom up processing: stimulus driven: example

You go to a grocery store and see that Hershey's released a new chocolate bar. You go and look at the nutrition label and determine that it was unhealthy after looking.

Top down processing: knowledge driven: example

Example: You go to a grocery store and see that Hershey’s released a new chocolate bar. Without looking at the label, you automatically associate that with it being unhealthy given your prior knowledge about hershey’s chocolates.

Activation level is greater for…

higher frequency words

Less activation is needed for…

higher than low frequency words to reach the response threshold

Interactive activation model: Response threshold

Minimum intensity of a stimulus required for it to be detected or to evoke a response in an organism

Interactive activation model: Spreading activation

Activating one concept in a network of associated ideas triggers a chain reaction that increases the activation of related concepts, making them more likely to be retrieved or recalled

Spreading activation example

Thinking of the word dog, and then associating that with pet, bone, bark because it activates related content

Interactive activation model: Decay

Natural weakening of memory due to lack of rehearsal and retrieval

Geon

basic geometric shape

Double dissociation

Where 2 distinct cognitive or behavioral processes are impaired in different individuals

Double dissociation example

language centers Broca’s area and Wernicke’s area. Damage in Broca’s area leads to difficulty speaking but with normal comprehension, and damage in the Wernicke’s area leads to the opposite results 

Fusiform face area

• Specialized for face recognition and perception 

• Also shows activity during tasks that require making subtle distinctions within a category (e.g., birds) 

• Not just for faces

Face inversion effect

People are significantly worse at recognizing and remembering faces that are presented upside down compared to those that are upright

Face inversion effect: Thatcher Illusion

phenomenon where modifications to an upside-down face, such as a rotated mouth and eyes, are not easily noticeable until the face is flipped upright, at which point the changes appear grotesque.

Selective attention

ability to select certain stimuli in the environment to process, while ignoring others

Dichotic listening?

Abilitly to process different sounds simulaneously presented to each ear

What is the shadowing task?

multiple people talk, how well you can listen to speaker you should pay attention to while ignoring other stimuli, say out loud what you hear as you hear it 

Typical results of the shadowing task

Participants notice the physical properties of the ignored message, but not its semantic content 

Can detect the physical properties of the message -> boy or girl, music or talking but can’t understand the message/ like can’t tell if its coherent

Cocktail party effect

phenomenon describing an individual’s ability to focus on one auditory stimulus (like a conversation) while ignoring other competing sounds or conversations in a noisy environment 

What does the cocktail party effect demonstrate?

selective auditory attention bc filtering relevant info and tune out distractions although highly significant stimuli -> if something has a really close relation to you (your name, your pet’s name, hometown, etc) (name: you hear often and probably recently) -> can still capture attention despite being in an “unattended” stream

Early vs. late selection

Load theory

more processing capacity is left for processing unattended input if the attended input is simple (low perceptual load) rather than complex (high perceptual load)

Processing capacity

 is limited, therefore we promote processing of attended stimuli and block processing of unattended inputs with a filter

Change blindness

Failure to notice a change in a visual scene, especially when the change happens during a visual disruption (like a flicker, blink, or quick cut).

Change blindness example

 In an experiment, participants watch two alternating images (a scene with and without an object). Many people don’t notice the missing/added object unless it’s pointed out.