Sensation is awareness of our surroundings (sound, color, form). Perception is interpreting this.
Senses
- Doctrine of specific nerve energies says that we have different senses because different signals received by sense organs stimulate different nerve pathways and go to different places in the brain.
- Synesthesia is a rare condition where people’s senses cross. Scientists have hypothesized that it’s a result of additional nerve connections.
- Absolute threshold: the smallest change in a sense (vision, hearing) that you can detect.
- Selective attention: the ability to focus on some parts of the environment and not others.
- We’re really good at not registering objects, to prevent sensory overload.
Vision
- Light has three dimensions:
- Hue: color, wavelength
- Brightness
- Saturation
- The front of the eye is protected by the cornea. Behind it sits a lens, which subtly changes its shape to focus. The amount of light allowed in is controlled by muscles in the iris, which surrounds the pupil.
- In the back of the eye, the retina, an extension of the brain (the tissue it’s formed from is from the brain).
- The more numerous receptors, rods, are sensitive to light. The other receptors, cones, are sensitive to color.
- Cones need lots lights, so color vision is worse in the dark.
- The optic nerve leaves the eye at the optic disc, where there are no rods or cones, which causes a blind spot.
- Feature-detector cells fire in response to specific features (horizontal lines, vertical lines, etc) to make up edges of objects.
- Others respond specifically to faces, hands, tools, words, numbers.
- Theories about vision:
- Trichromatic theory: color perception comes from having separate cones that are sensitive to blue, green, and red.
- Opponent-process theory: cells fire for opposite colors (blue/yellow, red/green).
- The cells that switch on or off to signal “green” send the opposite signal (“red”) when green is removed.
- Gestalt principles:
- Things closer together are grouped together (Proximity)
- The brain fills in gaps to create complete forms (Closure)
- Things that are alike are perceived as belonging together (Similarity)
- Lines and patterns are perceived as continuing in time or space (Continuity)
- Judging distances:
- Convergence: judging how much your eyes turn inward to focus on something close by.
- Retinal disparity: how different the views from your two eyes are.
Hearing
- The organ of Corti is the actual organ of hearing, which contains hair cells which are receptors.
- The hair cells rise and fall with sound, brushing against another membrane. The hair cells bending initiates a signal that’s sent along the auditory nerve.
Taste
- Papillae: tiny bumps on your tongue, whose sides are lined with taste buds.
- Actual taste receptors are inside taste buds (50-150 per taste bud).
Pain
- Gate-control theory
- Pain impulses must get past a (metaphorical) “gate” in the spinal cord.
- Gate = neural activity that blocks pain messages or lets them through
- When body tissue is injured, large fibers and damaged and small fibers open the gate, and pain messages can reach the brain.
- Stimulation (ice pack, heat) can interfere with pain by closing the gate.
- Phantom pain: pain experienced from parts of the body that have been amputated.
- Theory: other neurons have invaded the neurons that correspond to the amputated body part, and they are sending signals.
- Showing an amputee a mirror that creates the illusion of two healthy limbs can resynchronize signals and has been very effective.
Internal senses
- Kinesthesis tells us where our body parts are.
- Equilibrium is our sense of balance.
- Relies on semicircular canals in the inner ear.