8b sensation and perception pt 2

How does olfactory transduction begin?

• Airborne odorant molecules bind to receptor cells in the olfactory epithelium high in the nasal cavity

• Receptors convert chemical information into neural signals

• Signals pass through the olfactory bulb toward brain regions involved in identifying odors, emotion and memory

• Slide 4.

How can a relatively small number of olfactory receptor types represent many different smells?

• An odorant activates a pattern across multiple receptor types

• Different odorants produce different combinations and strengths of receptor activity

• The brain identifies odor from the overall pattern rather than requiring one unique receptor for every smell

• Slide 4.

What is anosmia, and how can aging or brain injury produce it?

• Anosmia is loss of smell • With age, olfactory receptor cells may be replaced less efficiently, reducing sensitivity • Head or brain injury can damage receptor axons, the olfactory bulb or central pathways • Trauma-related damage can be persistent and may also reduce flavour perception • Slide 4.

What structures support gustation?

• Papillae are visible structures on the tongue, and many contain taste buds • Taste buds contain receptor cells whose microvilli contact dissolved chemicals through a taste pore • Receptor activity is transmitted through nerve fibres to the brain • Not every papilla contains taste buds • Slide 5.

What are the five basic taste qualities, and why can cravings be informative?

• Sweet, sour, salty, bitter and umami • Taste signals can guide nutrient seeking and avoidance of harmful substances • A craving may reflect learning, expectation or sometimes a physiological need, such as seeking salt after depletion • Slide 5.

How do aging and expectation affect taste experience?

• Taste and smell sensitivity often decline with age, so stronger seasoning may be needed for the same experience • Perception also depends on expectation • Receiving an unexpected flavour can make an otherwise normal food seem unpleasant because top-down predictions conflict with the sensory input • Slide 5.

Why are smell and taste described as cross-modal partners?

• Taste receptors encode basic taste qualities while olfaction contributes much of a food's detailed flavour • The brain integrates signals from both systems into one experience • Loss of smell leaves basic tastes intact but makes foods seem less distinctive or flavourful • Slides 4-5.

Distinguish perceptual segmentation from object constancy.

• Perceptual segmentation separates one object from another and from the background • Object constancy lets us recognize the same object despite changes in size, orientation, lighting or viewpoint • Both help transform unstable retinal input into a stable world of recognizable objects • Slide 6.

What problems must the visual system solve to create a stable three-dimensional world?

• Each retina receives a flat two-dimensional image • Optical processing and cortical mapping involve predictable inversions • Retinal size and shape change with distance and viewpoint • The brain uses depth cues, object constancy and organizational rules to infer a unified three-dimensional scene • Slide 6.

What is binocular disparity, and when is it most useful?

• Each eye views the world from a slightly different position • The brain compares the two retinal images to infer depth • Disparity is greatest for nearby objects and decreases with distance • It is a binocular cue because it requires both eyes • Slide 7.

How do linear perspective, vanishing point and familiar size provide depth information?

• Linear perspective: parallel lines appear to converge with distance • Vanishing point: apparent location where converging lines meet • Familiar size: if a known object creates a smaller retinal image, it is judged farther away • These are monocular cues because one eye is sufficient • Slide 7.

What is motion parallax?

• As the observer moves, nearby objects sweep across the retina rapidly and often appear to move opposite the observer • Distant objects shift more slowly • The brain uses this difference in apparent speed to estimate relative depth • Slide 7.

How do interposition and elevation signal depth?

• Interposition: an object blocking part of another is perceived as closer • Elevation: on a ground plane, objects positioned higher in the visual field are often perceived as farther away • Both provide monocular depth information without requiring actual movement • Slide 8.

How do shadowing and texture gradients signal depth and shape?

• Shadowing uses light and dark patterns to imply an object's contours, surface orientation and position • Texture gradient: nearby surfaces show larger, clearer texture elements, while distant texture appears denser and less detailed • Slide 8.

What is the central idea of Gestalt visual organization?

• The visual system organizes separate elements into coherent wholes rather than perceiving isolated fragments • Grouping rules provide likely interpretations of ambiguous input • These efficient assumptions usually help perception but can also create predictable illusions • Slide 9.

Explain proximity, similarity and common movement.

• Proximity: elements close together are grouped • Similarity: elements sharing color, shape or other features are grouped • Common movement: elements moving in the same direction are perceived as belonging together • Slide 9.

Explain closure, good continuation and good form.

• Closure: the brain fills missing boundaries to perceive a complete object • Good continuation: intersecting contours are interpreted as smooth, continuous paths • Good form: ambiguous input is organized into the simplest, most stable shapes • Slide 9.

Why do equal lines look different in the Muller-Lyer illusion?

• The oblique fins around each line act like contextual depth or perspective cues • The visual system applies size-scaling assumptions normally useful in three-dimensional scenes • As a result, identical central lines are perceived as different lengths • Slide 10.

How do the rod-frame and Zollner illusions distort orientation judgments?

• Rod-frame illusion: a tilted surrounding frame biases perception of whether an inner rod is vertical • Zollner illusion: short oblique segments make parallel lines appear tilted or nonparallel • Both show that orientation is judged relative to surrounding context rather than measured independently • Slide 11.

Why does a tilted Mystery Spot environment make people feel or appear abnormally slanted?

• Walls and floors provide misleading visual reference frames • Vision suggests a false vertical, while the vestibular system and gravity provide conflicting information • The brain often gives strong weight to visual context, producing distorted posture and orientation judgments • Slide 12.

What is a top-down effect on vision?

• Prior knowledge, expectations and beliefs guide interpretation of ambiguous sensory input • Once a meaningful object is suggested, its features become easier to detect in the same image • Top-down processing changes what we consciously see without changing the retinal stimulus • Slide 13.

Why are visual illusions scientifically valuable?

• They reveal the assumptions and shortcuts used by normal perception • A consistent error shows how the brain organizes incomplete or ambiguous input • Illusions therefore provide evidence that perception is an active inference, not a literal copy of sensory stimulation • Slides 9-13.

What is the McGurk effect?

• Visual speech information from a speaker's lips changes the speech sound a listener reports hearing • Conflicting visual and auditory syllables can produce a third perceived syllable • It demonstrates that speech perception integrates sight and sound rather than processing each sense independently • Slide 14.

How does the rubber hand illusion alter body ownership?

• The real hand is hidden while a visible rubber hand and the real hand are stroked synchronously • Matching visual and tactile timing makes the brain attribute the felt touch to the rubber hand • The rubber hand can then feel like part of the body, and a threat to it may provoke fear or a pain-like response • Slide 15.

What is Capgras delusion, and what does it reveal about face recognition?

• A person visually recognizes a familiar face but lacks the normal emotional feeling of familiarity • The mismatch is explained as the familiar person having been replaced by an impostor • It suggests that identifying a face and generating its emotional familiarity response depend on distinct but normally connected systems • Slide 16.