Exam 2

Kanizsa Illusion

 

Adelson's Checker-shadow illusion

 

Representations in the Head

  • Mental representation: the sense in which properties of the outside world (colors, objects, knowledge) are copied/simulated by cognition

  • Neural representation: the way in which properties of the outside world manifest themselves in the neural signal (different spiking rates for different stimuli)

Distinction between sensation and perception

  • Sensation: the effects of a stimuli's on the sensory organs

  • Perception: the elaboration and interpretation of a sensory stimulus based on, for example, knowledge of how objects are structured

 

Visual processing

  1. From eye to brain

  2. Optic nerve V1

  3. V1 to rest of the brain

 

The Occipital Lobe

 

Nervous System

  • CNS: brain and spinal cord

  • Peripheral: everything else

    • Sensory neurons: fibers that carry info from body to brain

    • Motor neurons: fibers that carry info away from brain to body

Peripheral nervous system: sensory neurons

  • Receptor: cells that transform energy from the environment into neural signals to send to the brain

  • Sensory neurons: receive info from receptors and send signals to the brain

    • Receptive field: region of space that elicits a response from a given neuron

 

Retina

Retina: the internal surface of the eyes that contains specialized cells

5 types of cells in the retina

  1. Photoreceptors

    • Convert or transduce light into neural signals

      • Rods: specialized for low levels of light intensity and are more active during nighttime

      • Cones: specialized for detecting different wavelengths of light from which the brain can compute color and are more active during daytime

  2. Bipolar

    • Receive synaptic input from either rods or cones and send information to retinal ganglion cells

  3. Ganglion

    • Receive input from bipolar cells and send action potentials to the brain through optic nerve

    • Code for various aspects of vision, such as color, intensity, contrast, and movement detection

  4. Amacrine

  5. Horizontal 

From eye to brain: retina

  • Blind spot: the portion of the retina where the optic nerve leave the eye

    • No rods or cones there

From optic nerve to V1

  • There are number of different pathways that originate form the eye to eventually carry information to visual cortex

  • Geniculostriate pathway is the main route

    • Goes through the lateral geniculate nucleus (LGN, in the thalamus) and terminates in the primary visual cortex (V1)

Geniculostriate pathway

  1. Light from the visual fields hits both eyes

  2. Information from the nasal portion of the eyes crosses at the optic chiasm

  3. Information from both eyes is processed in the LGN

  4. The information travels form the LGN through the optic radiations to V1

  5. Basic visual information, such as orientation, is processed in v1

 

Visual processing

  1. From eye to brain

  2. From optic nerve to V1

  3. From V1 to rest of the brain

 

Primary Visual Cortex (v1; yellow)

  • Receives projects from the LGN

    • Perceives basic visual information, such as orientation and direction

    • Sends other visual information to secondary cortical areas

  • Striate cortex

    • The very rear of the occipital lobe is where the LGN projects

    • The area has several different names: primary visual crotex, V1, area 17, or striate cortex (because of the striped pattern it takes on after staining)

    • It consists of 6 major layers, some having sublayers

Spatial Arrangment of v1

  • Retinotopic organization: neurons that are close together in v1 process info that’s close together in the visual field

  • Damage to parts of the v1 results in blinding for that corresponding region of space because of the retinotopic map

  • Damage to v1 is considered "cortical blindness" because the retina re still functioning normally

 

Hubel & Wiesel

  • Single cell recordings lead to a hierarchial view of vision in which simple visual features (point of light) are combined into more complex ones (adjacent opoints of light may combine to a line

 

Type of Neurons in V1

  • Simple cells: neurons that respond to light in a particular orientation (or points alongalways  that line)

  • Complex cells: neurons that respond to light in a particular orientation ubt do not respond to a single point of light

  • Hypercomplex cells: neurons that respond to particular orientations and lengths

    • Combine the responses of several complex cells

The Seeing Brain Part III

 

Type of Neurons in V1

  • Simple cells: neurons that respond to light in a particular orientation (or points along that line)

  • Complex cells: neurons that respond to light in a particular orientation but do not respond to a single point of light

  • Hypercomplex cells: neurons that respond to particular orientations and lengths

    • Combine the responses of several complex cells

  • The information derived in V1 forms the building blocks for more advanced responses of neurons higher up in the hierarchy

 

Visual processing

  1. From eye to brain

  2. From optic nerve to V1

  3. From V1 to rest of the brain

 

The simple "building blocks" of vision are sent from V1 to secondary cortical areas for more complicated processing (eg. Color. Motion)

 

Secondary Visual areas

  • Receive info from the primary visual cortex and derive complicated visual information

    • V2: "v1's assistant" helps process and communicated basic info from v1 to other brain regions

    • V3: don’t worry about it

    • V4: color perception

    • V5/MT: motion perception

 

Color Perception and Area V4

  • Why do we need a center in our brain that specializes in color given that the retina is sensitive to different wavelengths of light?

    • Wavelength depends on the combination of the light source type (daylight, electric light) and the color of an object

  • Area V4 tries to compute the color of the object by taking into account variations in lighting conditions

 

Color Constancy

  • " the dress " is an example of color constancy

    • Color constancy: the color of a surface is perceived as constant even when illuminated in different lighting conditions

Damage to Area V4

  • Achromatopsia: failure to perceive color, the world (or even dreams) appears in gray scale

    • Not the typical color blindness (deficient or absent types of cone cell in the retina)

  • Damage to area V4 results in "cortical color blindness" because the retinas are still functioning normally

 

Beyond Visual Cortex

  • Visual cortex (primary and secondary) extracts basic visual info- colors, movement, shapes, edges

  • Regions beyond the visual cortex receive this information to figure out

    • What the object is

    • Where the object is in space

Two streams hypothesis (Milner & Goodale)

  • Humans possess two distinct visual systems with their own stream of processing

    • Dorsal: "where/how? Pathway is responsible for the guidance of actions and where something is in space

    • Ventral: "what" pathway is responsible for recognition and form representation (including face recognition)

Model of Object Recognition

  • 4 broad stages

    1. Early visual processing (color, motion, edges)

    2. Grouping of visual elements into a mental representation

      1. Gestalt principles, figure-ground segmentation

    3. Matching the mental representation to knowledge in brain (structural descriptions)

    4. Naming the object (attaching meaning, retrieved from semantic memory)

Lateral Occipital Cortex (LOC) and Shape perception

  • LOC responds more to viewing objects than to viewing textures, but responds the same to real and made-up objects

  • TMS to LOC disrupts the ability to match objects by shape but not their orientation

 

Neural Substrates of Object Constancy

  • Different regions make different contributions to object constancy (constant shape, across views, constant name/concept))

 Face Recognition Model

Bruce & Young model generally mimics the broad stages of object recognition

  1. Structural encoding of basic visual features (early visual processing)

  2. Grouping elements into the mental representation of a face

  3. Matching the mental representation to one's own knowledge store

  4. Naming the face

Prosopagnosia

  • The inability to recognize familiar faces

    • Typically results from damage to the fusiform face area (FFA) or other regions in the ventral "what" pathway 

Why are faces special?

  • Relies on holistic versus part-based processing

  • The level of expertise to discriminate between faces is higher when compared to objects

    • Is that sally or sarah?

    • Is than an apple or a lime

  • Faces are distinct category compared to objects

    • Patient WJ and his sheep

    • Double dissociation exists between object and face recognition

 

The Hearing Brain

 

Hearing is more than detecting sound

  • It involves constructing a model of the world:

    • What objects do the sounds correspond to?

    • Where are they?

    • What do they mean?

The Nature of Sound

  • Sound is a change in air pressure over time, in the form of a wave

  • Physical sound waves consist of frequency & amplitude

  • Pure tones are single sinusoid waveform (rarely heard in reality)

  • More complex sounds can be described in terms of combinations of multiple sinusoids

    • Superimposed pure tone sinusoids of different frequencies, intensities, and phases

  • Constructive interference: two sounds waves are "in phase"

  • Destructive interference: two sound waves are "out of phase"

  • Frequency relates to pitch; amplitude relates to loudness

  • Pitch and loudness are psychological properties; frequency and amplitude are physical properties

Pitch is perceived

  • Musical notes typically contain a series of regularly spaced sinusoids

    • A piano note of 220 Hz can be described in terms of sinusoids at 220 Hz, 440 Hz, 660 Hz, and so on

  • The lowest component is termed the fundamental frequency (f0) and is the perceived pitch of a musical note

Pitch Constancy

  • Missing fundamental phenomenon: if f0 is missing from the series then the pitch is still f0

  • This is an example of pitch constancy: two notes with completely different physical characteristics have the same perceived pitch

From Ear to Brain

  • 3 layers: outer, middle, and inner

Middle Ear

  • The middle ear contains 3 bones which convert airborne vibrations to liquid-borne vibrations with minimal loss of energy

The Inner Ear

  • The bones of the middle ear cause vibrations on the oval window of the cochlea

  • Cochlea: part of the inner ear that converts liquid-borne sound into neural impulses

    • Basilar membrane: a membrane within the cochlea containing tiny hair cells linked to neural receptors

Pitch and the Basilar Membrane

  • Sound induces mechanical movement of the basilar membrane which initiates neural activity in the auditory nerve

  • The location on the basilar membrane that vibrates most strongly determines the perceived pitch of a sound

    • Towards base = higher pitch

    • Towards apex = lower pitch

Auditory Pathway

  • From the auditory nerve the signal travels to the

    1. Brain stem

    2. Midbrain

    3. Medial geniculate nucleus of the thalamus

    4. Primary auditory cortex (the core region or A1)

    5. Secondary auditory cortex (the belt region or A2)

    6. Secondary auditory cortex (the parabelt or A3)

The Hearing Brain

Auditory Cortex

  • Mostly in Heschl's gyrus in the temporal lobe

  • Information received by the core is sequentially processed by the belt, and then parabelt

    • Primary auditory cortex (A1): pure tones and sounds

    • Secondary auditory cortex (A2 & A3): complex sounds and sound patterns (including speech)

Auditory Pathway

  • The auditory pathway is not a passive transmission of information from the ear to the auditory cortex

  • It actively extracts and synthesizes of information in the auditory signal

Tonotopic Organization

  • The auditory nerve and auditory cortex have a tonotopic organization: sounds close to each other in frequency are represented by neurons that are spatially close to each other in the brain

Comparisons Between the Auditory and Visual System

Space

Auditory System

Visual System

Thalamo-cortical route

Medial geniculate nucleus projects to primary auditory cortex

Lateral geniculate nucleus projects to primary visual cortex

Organizing principle of early neural processing

Tonotopic organization (orderly mapping between sound frequency and position on cortex)

Retinotopic organization (orderly mapping between position on retina and position on cortex)

Temporal and spatial sensitivity

Temporal > spatial

Spatial > temporal

Functional specialization of feature processing

Less well documented in the auditory domain

Well documented for color and movement

Higher order context-dependent pathways

Evidence for separate auditory pathways for "what" versus "where/how"

Evidence for separate visual pathways for "what" versus "where/how"

Feature processing in Auditory Cortex:

Pitch

  • Evidence from single cell recordings:

    • Compared to vision, there is less evidence that different auditory features (loudness, pitch, tempo, timbre) are localized to individual regions

    • The strongest evidence points to a "pitch center" related to pitch constancy ins secondary regions

Loudness

  • There are also neurons that are tuned to loudness and location

Dual Auditory Streams

  • Some auditory neurons/areas are tuned for:

    1. Sound itself (irrespective of where it is coming from)

Or

  1. Where the sound is coming from (irrespective of what is heard)

"What" vs. "where"

  • Evidence from monkeys supports the "dual stream" hypothesis for audition

    • Anterior belt responds to monkey calls (irrespective of location)

      • The beginning of the "what" pathway along the temporal lobes

    • Posterior belt responds to location of sounds (irrespective of who is making it or what the sound is)

      • The beginning of the "where/how" pathway to the parietal lobes

Music Perception

  • Music considered a "human Instinct" by some (universal, emerges without training)

  • The evolutionary function of music remains uncertain

  • Musical systems use. Aset of discrete pitches presented in patterns that vary over both pitch (melody) and time (rhythm, tempo)

  • Music, like vision or language, may be decomposed into different mechanisms

Congenital Amusia

  • "tone-deafness"/congenital amusia: a developmental difficulty in perceiving pitch relationships

    • Inability to detect when someone sings out-of-tune, recognize familiar songs and sing without the help of lyrics, and maintain songs in memory

    • Congenital means " Present from birth"

  • Emerges from birth in the absence of

    • Speech delay

    • Intellectual deficiencies

    • Acquired brain damage

    • Music deprivation

  • Linked to increased grey matter in auditory cortex and frontal regions

  • Reduced connectivity: reduced white matter in the right arcuate fasciculus

 Basic Cognitive Framework for movement and Action

  • Movement: physical moving of the body

  • Action: a movement which results from cognitive processing that coordinates the needs of a person withing their current environment

  • Actions are theorized to be carried out by coordinating motor programs

  • Motor programs code for general aspects of movement to increase computational efficiency

    • Timing of different movement components

Movement, Action, and Self

  • Somatosensation: perceptual processes that relate the skin and body

    • Touch, pain, heat, limb position

  • Proprioception: knowledge of position of limbs in space

  • Sensorimotor transformation: linking together perceptual knowledge of the environment and knowledge of one's body to enable action in the environment

    • Somatosensation + proprioception = sensorimotor transformation

The Frontal lobes in Movement and Action

  • Premotor areas assist w/ preparing actions (movement and action)

    • Frontal eye fields: voluntary movement of the eyes

    • Lateral Premotor cortex: links action w/ visual objects in the environment

    • Medial premotor cortex "supplementary motor area" responsible for self-generated actions

  • Prefrontal cortex is generally involved with planning and higher order cognition (not just actions)

    • After the premotor cortex prepares an action, the prefrontal cortex:

      1. Mediates the selection of actions

      2. Maintains the goal of the action

  • Primary Motor Cortex (M1) Homunculus

    • Somatotopic organization: specific areas of M1 control specific parts of the body

    • Body parts that perform precise movements, like the hands and face, are disproportionately large in the motor homunculus

    • Contralateral processing

  • Subcortical Movement Generation

    • Subcortical structures play an important role in movement, particularly w/ the preparation and execution of actions

      • Help se the particular parameters (force and duration) of a planned or in progress movement

      • 2 distinct subcortical pathways

        • Cerebellar loop

        • Basal ganglia circuit

  • Disorders of the Basal Ganglia

    • 2 general categories

      1. Hypokinetic: reduction in movement

        • Parkinson's Disease

      2. Hyperkinetic: increase in movement

        1. Huntington's Disease

        2. Tourette's

    • Excitatory and inhibitory neurotransmitters show dysregulated signaling -- and so does dopamine

Parkinson's Disease

  • Mean on sent around 60 years

  • Affects 0.15% of the population

  • Dopaminergic brain cells are lost in the pathways linking the substantia nigra and basal ganglia

  • Results in both motor and cognitive deficits

  • Motor symptoms

    • Lack of spontaneous movement

    • Slowness of movement

    • Walking degenerates to a shuffle

    • Failure to scale muscle activity to movement amplitude

    • Rigidity

    • Tremor

  • Cognitive deficits

    • Attention

    • Speed of processing

Why does loss of dopaminergic cells in the basal ganglia lead to Parkinon's Disease?

  • The loops connecting the basal ganglia and thalamus consist of two complementary routes

    • Direct route "accelerator": promotes action (increases activity in cortex)

    • Indirect route "brake" : inhibits action (decreases activity in cortex)

  • Lesions between the substantia nigra & basal ganglia result

 

What are emotions?

  • Emotion: a state associated w/ stimuli that are rewarding or punishing, that often has survival value

    • Affective vs nonaffective stimuli

  • We use emotions through our own experiences, the mindset of others, and by sharing them w/ others

Characteristics of Emotions

  • A state we would like to obtain or avoid (rewarding vs punishing)

  • Transient but stored in long-term memory

  • Emotional stimuli draw attention to themselves

  • Have hedonic value (subjectively liked or disliked)

  • An internal bodily response (sweating, increased heart rate)

  • External motor outcomes (smiling, muscles tensing)

 

 

 

The general framework and neurobiology of emotions

 

Darwins view of emotion (late 1800s)

  • Documented the evolution and outward menifestation of emotions

    • The expression of the emotions in man and animals

  • Expression: external motor outcomes in the face and body associated w/ emotional states

  • He believed expressions were inantve and conserved by evolution

Freud's view of emotion (1920)

  • Our minds are divided into 3 different mechanisms

    • Id: primitive urges and basic instinctual drives

    • Ego: decision maker of the mind, balances id and super ego

    • Super-ego: ideal, based on cultural norms, aspirations, and norms

  • Emotions unconsciously bias our behavior

Two theories of Emotion

James-Lange Theory

  1. Sensory stimulus (you see a snake)

  2. Emotional bodily state (person puts their hands up in fear)

  3. Emotional perception/interpretation (fear) (body sees you react scared, so your brain determines youre scared)

Cannon-Bard Theory

  1. Sensory stimulus

  2. Emotional perception/interpretation (fear) (youre scared)

  3. Body responds accordingly (emotional bodily state)

Neurobiology: mediated by the peripheral nervous system

 

James-Lange Theory of Emotion

  • The conscious self-perception of bodily changes produces emotional experience

  • Changes in a bodily state occur before the emotional experience

    • Im sad due to the physical response of me crying

    • My heart rate increased and I began sweating, now Im scared

Canon-Bard theory of emotion

  • The conscious experience of emotion is experienced, and then the body responds

  • Changes in bodily state occur after the emotional experience

    • Im experiencing sadness so I started crying

    • I got scared so now my heart rate is increased and Im sweating

How neurobiology mediates responses based on the two theories of emotion

  • James Lange: the involuntary part of the PNS triggers the perception of emotion

    • Contrary evidence: injection of adrenaline doesn’t lead to the experience of emotion

  • Canon-Bard

    • The theory was inspired by neurobiology and hypothesized the hypothalamus is the centerpiece of emotions

      • Animals still exhibit emotional expression after removal of the cortex

      • Hypothalamus receives and evaluates sensory inputs based on emotional conent, and communicated to 1 the autonomoic system and 2 the cortex

  • The papez Circuit and the Limbic system

    • Cingulate cortex

    • Hippocampus

    • Hypothalamus

    • Anterior nucleus of thalamus

  • "emotional brain" = Papez circuit + amygdala & orbitofrontal cortex

  • No longer considered totally accurate

Basic Emotions

  • Ekman: 6 basic emotions that occur in humans automatically

    • Happiness

    • Sadness

    • Disgust

    • Anger

    • Fear

    • Surprise

  • Believed the 6 emotions were independent of culture and had their own neural basis and evolutionary purpose

Constructed Emotions

  • Barrett et al: emotions are constructed because they require information outside of the emotional system

    • All emotions tap into a core affect organized across 2 dimensions

    • Bodily feelings of emotions are linked to limbic structures

    • Facial expressions are constructed based on culture and experience

  

Can you die of a "broken heart"?

  • The same brain networks are used to process both social stimuli and nonsocial stimuli with affective properties

 

The Brain regions responsible for emotional and social functioning

  • Emotional brain network

    1. Amygdala

      • Medial structure at the tip of the left and right temporal lobes that is anterior to the hippocampus

      • Part of the limbic system

      • Shaped like an almond

      • Responsible for basic fear response

        1. You see scary snack

        2. Thalamus takes the info and goes to visual cortex and amygdala at the same time (multiple visual networks)

      • Fear conditioning

        • During learning, the tone becomes associated with the shock

        • The rat experiences fear when it hears the tone, even if the shock does not follow the tone

        • Lesioning the amygdala in mice reverses fear conditioning

      • The "master coordinator" of threat memory

      • Kim et Al

        • The basolateral amygdala (BLA) contains 2 populations of neurons that are genetically programmed to encode eitehr fearful or happy memories

          • Anterior neurons were programmed for "happiness" and showed conditioning to female stimuli (reward)

          • Posterior neurons were programmed for "fear" showed and conditioning to being shocked (avoidant)

      • Lesions of the amygdala in monkeys

        • Bilateral amygdala and temporal lesions in monkeys causes Kluver-bucy syndrome:

          • Unusual tameness

          • Emotional blunting

          • Tendency to examine objects w/mouth

          • Dietary changes

        • Loss of 'emotional value'

        • The role of the amygdala is complicated and not simply just the "fear center" of the brain

      • Amygdala and perception of fear in humans

        • Patient DR suffered bilateral amygdala damage and displayed difficulty with recognizing fearful expressions

          • Impaired at recognizing fear

          • Could imagine famous people but not their fearful expressions

          • Difficulty in identifying vocal emotional expressions

        • The amygdala showed greater fMRI activation in response to in unconsciously fearful stimuli

          • Demonstrated in healthy participants and a patient w/ damage to their amygdala

      • Summary

        • Coordinates the response to fear and fear related events

        • Assists with learning and long-term memory storage that is emotional

        • Evaluates the value of stimuli to make emotional associations

          • Positive and negative valence

    2. Anterior cingulate cortex

      • Located in the medial prefrontal cortex

      • Social-emotional functions

        • Response evaluations

          • Assess the value of a response

          • Determine if an action is a reward or punishment

        • Autonomic response

          • Skin conductance response, heart rate, blood presure

        • Pain

      • Pain and the anterior cingulate cortex

        • Receives pain sensory input from thalamus

        • Regulates feelings of pain

          • Connects to areas rich in endogenous opioids

        • Empathy

          • Increased fMRI activation when watching someone in pain

        • Implicated in "emotional pain"

          • Separated from a loved  one

          • Socially excluded

    • Insula

      • Small "island" of cortex buried beneath the temporal lobes

      • Interoception

        • Monitoring the internal state of the body

      • Functionally specialized to process disgust

Insula and "disgust"

  • Types of disgust

    • Physical bad taste

    • Interpreting facial expressions

    • Moral disgust

  • Orbitofrontal Cortex

    • Located in the prefrontal cortex

    • Computes the current value of a stimulus within the current context

    • Helps to quickly change behavior to rewarding or non-rewarding stimuli

    • Contextualize emotions

      • Linked to subjective reports of pleasantness

  • Ventral striatum

    • Located in the basal ganglia and connects to the orbitofrontal cortex

    • Specialized for emotions and calculating the probability of reward in social and non-social contexts

      • Connects to the frontal cortex to increase or decrease probability of reward

      • Encodes the difference between predicted reward and actual reward