processing the environment - MCAT

Visual cues

features that the brain uses to organize and interpret sensory information

Binocular cues

visual cues that require both eyes working together

Retinal disparity: brain calculates difference between what left & right eye see, bigger difference = closer object

Convergence: eyeballs turn inward when you focus on very close object; eyes converge more = closer object

Monocular cues

visual cues that only require one eye

Relative size

Interposition

Relative height

Relative motion / Motion parallax

Shading

Linear perspective

Texture gradient

Relative clarity

Weber’s Law

The change needed to notice a difference in a stimulus is always a constant proportion of the original stimulus’s intensity

K = ΔI / I

K = constant specific to sense being measured, “Weber fraction”

ΔI = just-noticeable difference

I = initial intensity

Absolute threshold of sensation

minimum intensity required to notice stimulus 50% of the time

• influenced by psychological state, expectations, experience, motivation, alertness, etc.

• stimuli with lower intensities than ATS are subliminal

Somatosensation

Body’s sensory system for:

Temperature — Thermoception

Pain — Nociception

Pressure — Mechanoreception

Movement/position — Proprioception

Sensory receptor adaptation types

Differ based on what happens to firing rate when exposed to continuous unchanging stimulus

• Fast-adapting receptors fire intensely when stimulus begins, then quickly level off to nothing (eg. thermoceptors)

• Slow-adapting receptors fire rapidly when stimulus begins, then slowly level off, continuing to fire at steady low rate. (eg. nociceptors)

• Non-adapting receptors fire steadily, unchanging as the stimulus itself (eg. chemoreceptors)

Vestibular system

Sensory network in inner ear that controls balance and spacial orientation

Semicircular canals (anterior, posterior and lateral) containing endolymph that shits w/ movement

• detect rotational movement & angular acceleration

Otolith organs (Utricle & Saccule) containing calcium crystals attached to hair cells in gel

• detect linear acceleration, gravitational pull and head tilt

Signal detection theory

explains how we make decisions under uncertainty

Detection of signal depends not only on intensity but also on background distractions (noise) and observer’s psychological state

• 4 outcomes: Hit (true positive), Miss (false negative), False alarm (true positive), Correct rejection (true negative)

• d’ (sensitivity): represents the strength of signal relative to background noise. Higher d’ → easier to distinguish signal → noise and signal distributions are further apart

• C or β (Criterion / Bias): represents the observer's psychological threshold or strategy, based on expectations and the consequences of their choices.

  • Liberal Strategy: (lower C) The observer says "yes" to almost everything to ensure they never miss a signal. This increases hits but also leads to more false alarms.

  • Conservative Strategy: (higher C) The observer only says "yes" if they are absolutely certain. This reduces false alarms but results in more misses.

Receiver-Operating Characteristic (ROC) Curve

Illustrates trade-off between sensitivity and specificity

• true positive on y axis, false positive on x

Bottom-up vs. Top-down processing

Stimulus influences perception, data-driven

vs.

Expectations and prior knowledge influence perception

Gestalt principles

Explain how our brains naturally organize visual elements into organized patterns and recognizable shapes

Succ Fat PP, Chew Colossal Cherry

Similarity: group similar objects together

Figure-Ground: ability to separate into figure (closer, distinct shape) and ground (background, indistinct)

Proximity: group close objects together

Pragnanz: reduce reality to simplest form

Continuity: lines are seen as following smoothest path

Common Fate: group together objects moving in same direction

Closure: objects grouped together are seen as a whole

The Gestalt principles of grouping hold that …

… the brain processes the whole rather than the sum of its parts

Aβ vs. Aδ fibers

Large, thickly myelinated. Quickly transmit touch, pressure, vibration

vs.

Small, thinly myelinated. Transmit temperature and pain slower.

5 types of mechanoreceptors

“How’s My Pretty Mechano Receptor”

Hair Follicle Receptor

Meissner’s Corpuscle

Pacinean’s Corpuscle

Merkel’s Disc

Ruffini’s Corpuscle

All work by allowing influx of Na⁺ one way or another

Hair Follicle Receptor

• structure/function

• location

• type of touch

When hair bends, opening created to receptor, allowing influx of Na⁺

• located in reticular dermis

• senses changing light pressure on hairy skin (no way)

senses changing light pressure because area around hair

Meissner’s Corpuscle

Looks like a beehive

Changing light pressure displaces disc, movement allows influx of Na⁺

• located in papillary dermis

• only mechanoreceptor to be absent in hairy skin (only works in glabrous skin)

Pacinian’s corpuscle

Looks like an onion and has the rings to boot

Changing deep pressure spins rings, allowing influx of Na⁺

• Located in hypodermis

Merkel’s disc

Modified epithelial cell which contains vesicles filled with peptides

Pressure causes vesicles to burst and release peptides, which bind to receptor and trigger influx of Na⁺

located in stratum basale — papillary dermis, senses sustained light pressure

Ruffini’s Corpuscle

looks kinda like a mushroom

Senses sustained deep touch

located in reticular dermis

Full of collagen, deep touch stretches collagen allowing influx of Na⁺