Auditory Localization and Binaural Cues

• Sounds from various locations create an auditory space.
• Locating sound sources in auditory space is called auditory localization.
• The cochlea is stimulated based on sound frequencies, causing nerve firing patterns and the perception of a tone's pitch and timbre.
• Activation of nerve fibers in the cochlea relies on the frequency components of tones, not their origin.
• Location cues are created by sound interaction with the listener's head and ears.

Binaural Cues

• Binaural cues involve sounds more intense at one ear and reaching that ear sooner when located off to the side.
• Interaural level difference is the difference in sound pressure level reaching each ear.
• The head acts as a barrier, creating an acoustic shadow, which affects high-frequency sounds.
• A boat analogy and water ripples analogy describe the interaural level difference.
• When the distance to each ear is equal, sound arrives simultaneously, resulting in a zero interaural time difference.
• Interaural time difference is the time difference between when sound reaches each ear.
• Sounds from directly ahead arrive at each ear simultaneously, resulting in zero time and level differences.
• Sounds shifted to one side reach the closer ear first.
• Low frequencies do not create acoustic shadows

Cone of Confusion

• Sounds from various positions can cause ambiguity.

Spectral Cues

• Spectral cues involve elevation, utilizing the pinnae.
• Training with molds creates new correlations between spectral cues and location, while old correlations persist.

3D Sound Perception

• Azimuth refers to left to right.
• Elevation refers to up and down.
• Distance refers to how far away a sound is.

Jeffress Model

• The Jeffress model of auditory localization suggests that neurons are wired to receive signals from both ears.
• Neurons fire when signals from both ears reach them simultaneously; these are called coincidence detectors.
• The Jeffress model proposes a circuit with a series of ITD detectors, each tuned to a specific ITD.
• ITD tuning curves plot a neuron's firing rate against the ITD.
• Bird neurons are sharply tuned, while mammal neurons are broadly tuned.

Cortical Mechanism of Localization

• Pioneering studies involved cats locating food boxes at varying distances.

• Cats were rewarded for correctly approaching the sound of a buzzer.

• After learning the localization task, lesioning auditory cortex areas impaired the ability to relearn how to localize sounds.

• The anterior belt area perceives complex sounds.

• The posterior belt area localizes sounds.

• The "what" auditory pathway goes from anterior belt to the front of the temporal lobe to the frontal cortex.

• The "where" auditory pathway goes from the posterior belt to the parietal lobe to the frontal cortex.

• The precedence effect is when a single sound appears to originate from near the lead speaker.

• Architectural acoustics relate to how indirect sound changes the sound quality in rooms.

Factors Affecting Acoustics

• Room size affects acoustics and sound perception.
• The amount of sound absorbed by walls, ceiling and floor influences acoustics.
• Reverberation time is how long sound takes to decrease to 1/1000th of its original pressure.
• Leo Beranek studied acoustics in 20 opera houses and 25 symphony halls in 14 countries.
• Intimacy time is the time between direct sound and the first reflection.
• Bass ratio is the ratio of low to middle frequencies reflected from surfaces.
• Spaciousness factor is the fraction of indirect sound received by a listener.
• Concert halls perform better with a reverberation time of 1.5 seconds
• Intimacy times of about 20 msec and high bass ratios and spaciousness factors correlate with acoustics

Auditory Scene

• Auditory scene is the array of sound sources at different environmental locations.
• Simultaneous grouping organizes sounds that occur at the same time.
• Sequential grouping organizes sounds that occur one after another.
• Onset synchrony suggests that sounds starting at different times likely come from different sources.
• Sounds with the same timbre or pitch range are often produced by the same source.
• Perception is predictive.
• The brain uses prior experience to predict what's likely in the environment.
• Grouping principles are part of this predictive process.
• Relying on one cue can lead to illusory perceptions.
• Multiple cues working together create a more reliable perception.

Similarity of Pitch

• Consecutive sounds with similar pitch are grouped together.
• Similar pitch helps us perceive sequences from the same source.
• Large pitch differences lead to separation into different streams.

Auditory Stream Segregation

• Slow alternation of high/low tones are perceived as one stream.
• Fast alternation of high/low tones are perceived as two separate streams.
• Grouping depends on pitch and tempo.

Scale Illusion / Melodic Channeling

• Notes alternating in pitch are sent to each ear.
• Perception reorganizes notes into smooth melodies based on pitch similarity, not actual ear input.

Auditory Continuity

• A continuous tone interrupted by silence is perceived as stopping.
• When gaps are filled with noise, the tone is perceived as continuing.
• It's similar to visual good continuation.

Experience & Melody Schema

• Familiar melodies can be recognized even when distorted if listeners have prior knowledge.
• This demonstrates the influence of memory and learned grouping patterns.
• Ventriloquism effect, or visual capture

Two-Flash Illusion

• A single dot flashed on the screen is perceived as one flash.
• If the single dot is accompanied by two beeps, the participant sees two flashes, even though the dot was flashed only once.
• Speechreading (lipreading) enables deaf people to determine what people are saying by watching their lip and facial movements.
• Receptive fields of neurons in the monkey’s parietal lobe respond to auditory and visual stimuli that are located in the same area.
• Echolocation uses tongue clicks to locate nearby objects.
• The visual area can activate spatial experiences and echoes from specific positions in space.

Chemical Senses

• Taste involves receptors in the tongue.
• Olfaction involves stimulation of receptor neurons in the olfactory mucosa, located on the roof of the nasal cavity.
• Flavor is a combination of taste and olfaction.
• Neurogenesis: Olfactory receptor replacement takes 5–7 weeks, while taste receptors are replaced in 1–2 weeks

Taste Qualities

• Sodium chloride tastes salty.
• Hydrochloric acid tastes sour.
• Sucrose tastes sweet.
• Quinine tastes bitter.
• Potassium chloride has salty and bitter components.
• Sodium nitrate tastes salty, sour, and bitter.
• Sweet flavors cause acceptance.
• Bitter flavors cause rejection.

Taste System

• Filiform papillae are cone-shaped and cover the entire surface of the tongue.
• Fungiform papillae are mushroom-shaped and located on the tip and sides of the tongue.
• Foliate papillae are folds located on the side and back of the tongue.
• Circumvallate papillae are flat mounds shapes on the back of the tongue.
• The tongue contains papillae, taste buds, taste cells, and receptor sites.
• Filiform papillae are the only ones that don't contain taste buds.
• The middle of the tongue causes no taste
• The tongue has around 10,000 taste buds.
• Taste buds have 50-100 taste cells.
• Transduction occurs when chemicals contact receptor sites on taste cells.

Taste Nerves

• The chorda tympani nerve is from taste cells on the front and sides of the tongue.
• The glossopharyngeal nerve is from the back of the tongue.
• The vagus nerve is from the mouth and throat
• The superficial petrosal nerve is from the soft palate and the top of the mouth.
• The tongue, mouth, and throat connect in the brainstem's nucleus of the solitary tract.
• Signals travel to the thalamus and then to the insula and frontal operculum in the frontal lobe.

Flavor Coding

• Across-fiber patterns/population coding
• Erickson reasoned that if taste quality depends on the across-fiber pattern, then two substances with similar patterns should taste similar.
• Evidence for specific taste receptors has been obtained via genetic cloning.
• Sweet blindness occurs when cats lack a functional gene for forming a sweet receptor.
• Mueller’s experiments on specificity coding.
• 6-n-propylthiouracil, or PROP, has properties similar to those of PTC.
• Anosmia is losing sense of smell

Smell Quantification

• Microsmatic vs. Macrosmatic
• Detection odors.
• Detection threshold is the lowest concentration at which an odorant can be detected.
• The forced-choice method uses one trial with a weak odorant and another with no odorant.
• Difficulty identifying odors may be due to an inability to retrieve the odor's name from memory.
• COVID molecules attach to ACE2 enzymes in the intestines, lungs, arteries, heart, and nose.
• CE2 is on sustentacular cells, providing metabolic and structural support to olfactory sensory neurons.
• Covid attacks the supporting cells.

Odor Qualities

• α-ionone smells like violets.
• Difficulty in relating odors to molecular properties: similar structures can smell different, and vise versa.
• Odor objects.
• The first stage of olfaction occurs in the olfactory mucosa and olfactory bulb via analysis that transforms components into neural activity.
• The second stage of olfaction occurs in the olfactory cortex and beyond via synthesizing information about chemical components.
• The olfactory mucosa is on the roof of the nasal cavity below the olfactory bulb.
• Olfactory receptor neurons in the mucosa are dotted with olfactory receptors.
• Each olfactory receptor type is sensitive to a specific odorant range.
• There are 400 different types of olfactory receptors, each sensitive to a particular group of odorants.
• There are 10,000 of each type of ORN.
• There are 1,000 types in the mouse
• Calcium imaging identifies when an olfactory receptor responds by measuring calcium ion increases.
• The recognition profile is the pattern of activation for each odorant.
• Glomeruli receive signals from ORN.

Olfactory Maps

• Chemotopic maps are odorants organized by molecular features like carbon chain length.
• Odor maps (odor quality).
• Odotopic maps.
• Signals are transmitted in the cortex.
• The piriform cortex (PC) is the primary olfactory area, and the orbitofrontal cortex is the secondary area.
• The olfactory bulb activates specific areas, forming a spatial "odor map" that disappears in the piriform cortex (PC).
• The piriform cortex likely uses a distributed coding system for complex odor recognition and memory.
• Repeated experience links activations into an "odor object."
• Odor perception relies heavily on experience and learning
• Olfaction can trigger vivid autobiographical memories - Proust effect
• People report stronger emotions and a greater sense of “being transported back in time” in the first decade of life.
• Olfactory system closely connects to the amygdala and hippocampus.
• The retronasal route goes from the mouth through the nasal pharynx.
• Food and drink stimulate tactile receptors in the mouth, creating oral capture
• The orbitofrontal cortex contains many bimodal neurons.
• This area helps create flavor perception.
• The insula is also involved in this process.
• Participants rated the same wine as tasting better when it was labeled $90 rather than $10.
• A "cheddar cheese" odor was rated more pleasant than a "body odor” with greater OFC activation.
• A red strawberry dessert was rated sweeter and more flavourful on a white plate than a black plate.
• Café latte tasted sweeter from a blue mug than a white one.
• Even the shape of a wine glass can affect how wine flavor is perceived.
• Flavor perception and brain response are influenced by hunger and satiety.
• The pleasantness and orbitofrontal cortex response to a banana odor (food) drops after eating-sensory-specific satiety
• Frontal cortex helps determine the reward value of food.
• Chemical senses serve more than just creating sensory experiences-they help guide behaviour, crucial for survival.

Chemical Sense Interactions

• Matching across senses
• Influences: alteration of perception; red plate -> food taste sweeter
• Multimodal interaction
• Flavor results from combined taste and smell.

Associations

• Fruits are matched by high pitches, and smells such as smoked, musk, and dark chocolate are matched by lower pitches.
• Pineapple is associated with red, yellow, pink, orange, and purple, whereas caramel is associated with brown, orange, and pale orange.
• Citric acid and sucrose are matched to high tones, and coffee and MSG are matched to lower tones
• Texture of fabric is softer with lemon scents, unpleasant animal smells cause the reverse.
• Smooth, consonant music = chocolate creamier & sweeter and harsh music = chocolate less pleasant.
• cherry drink appears orange if orange-coloured and is rated as less peasant when coloured orange instead of red
• Even wine experts mistook a normal wine for a rose version if colour was modified.
• Citrus improves attention to cleaning while coffee boosts reasoning skills based on the learned response
• Bright colours = happiness = pleasant smells.
• Infants like the taste of water more if their mothers drank carrot juice during pregnancy and lactation.