6b sensation and perception pt 1

Distinguish sensation, transduction and perception.

• Sensation: receptors detect physical environmental information • Transduction: receptors convert physical energy into neural signals, such as light in vision or pressure waves in hearing • Perception: the brain interprets those signals into meaningful experience • Intact sensation can coexist with impaired perception after cortical damage • Slide 3.

Match the three major properties of light waves to visual experience.

• Wavelength: perceived as color or hue • Amplitude: perceived as brightness • Purity: perceived as saturation or richness of color • Visible light occupies only a small portion of the electromagnetic spectrum • Slide 5.

What are the main functions of the cornea, iris, pupil, lens, retina and optic nerve?

• Cornea: transparent surface that begins bending incoming light • Iris: colored muscle controlling pupil size • Pupil: opening regulating how much light enters • Lens: changes shape to focus light • Retina: contains light-sensitive receptors • Optic nerve: carries retinal output to the brain • Slide 6.

What is accommodation, and why does the retinal image not appear upside down?

• Accommodation: lens changes curvature to focus objects at different distances on the retina • Cornea and lens refract light so the retinal image is inverted and reversed • The brain interprets this predictable input as an upright, stable world • Slides 6-7.

Compare myopia and hyperopia, including their corrections.

• Myopia or nearsightedness: eye is too long or focusing power too strong, so distant images focus in front of the retina • Corrected with a concave lens • Hyperopia or farsightedness: eye is too short or focusing power too weak, so images focus behind the retina • Corrected with a convex lens • Slide 7.

Compare cataracts and glaucoma.

• Cataract: lens becomes cloudy, producing generalized blurry or hazy vision; treated by replacing the cloudy lens • Glaucoma: elevated intraocular pressure damages the optic nerve, commonly beginning with peripheral vision loss • Cataract disrupts light transmission; glaucoma damages neural output • Slide 8.

What is macular degeneration, and how does its visual deficit differ from glaucoma?

• Degeneration of the macula, often associated with advanced age • Compromises central, detailed vision while peripheral vision may remain • Glaucoma typically begins with peripheral loss, whereas macular degeneration targets the center of vision • Slide 8.

Compare rods and cones and explain why the fovea produces the clearest vision.

• Cones: color and high-acuity detail; concentrated in the fovea and macula • Rods: highly sensitive in dim light and important for peripheral and motion detection • The fovea is densely packed with cones and has minimal convergence, producing detailed central vision • Slide 9.

Why is rod-rich peripheral vision useful even though it has less detail?

• Peripheral rods detect dim stimuli and movement efficiently • They alert you to events outside the current focus and redirect attention toward them • Processing every part of the visual field at foveal-level detail would require far more neural resources • Slide 9.

What causes common red-green colorblindness, and why can affected people still use traffic lights?

• Usually caused by altered or absent cone photopigments, making red and green signals harder to distinguish • It is more common in males because common forms are X-linked • Traffic lights can also be identified by their consistent spatial positions, so performance need not depend only on color • Slide 10.

Give the ordered sequence of visual transduction within the eye.

• Light enters through cornea and pupil • Lens refracts it toward the retina, creating an inverted image • Rods and cones convert light into neural activity • Bipolar cells receive photoreceptor output • Ganglion cells summarize it and their axons form the optic nerve • Information exits at the optic disc • Slide 11.

What is the physiological blind spot, and why is it usually unnoticed?

• The optic disc is where ganglion-cell axons leave as the optic nerve • It has no rods or cones, so that retinal location cannot detect light • Continuous eye movements and the brain's use of surrounding and opposite-eye information fill in the missing region • Slide 11.

Why do bipolar and ganglion cells consolidate retinal information?

• Many photoreceptors converge onto fewer downstream cells • Consolidation reduces the amount of information that must leave the eye • It emphasizes useful patterns rather than transmitting every receptor independently • Greater convergence increases sensitivity but reduces fine spatial detail • Slide 12.

What is a visual receptive field?

• The specific region of the retina or visual environment that changes a neuron's activity • A ganglion cell summarizes the pattern detected by photoreceptors within its receptive field • Receptive fields let the visual system encode local contrast and spatial patterns • Slide 12.

What does trichromatic theory propose about color vision?

• Color begins with three cone classes most sensitive to short, medium and long wavelengths • The brain compares their relative activity • Different patterns across the three cone types generate the perception of many colors • Slide 13.

What does opponent-process theory propose about color vision?

• Later visual neurons organize color into opposing channels • Major pairs are red versus green, blue versus yellow and black versus white • Activating one side of a channel inhibits the opposing side • Trichromatic and opponent processing describe different stages and are complementary, not competing explanations • Slide 13.

What route does visual information take after leaving the retina?

• Ganglion-cell axons form the optic nerve • Some fibres cross at the optic chiasm • Information travels to the lateral geniculate nucleus or LGN of the thalamus • The LGN processes and relays it through optic radiations to primary visual cortex or V1 in the occipital lobe • Slide 14.

How are visual fields represented across the two cerebral hemispheres?

• Information from the left visual field of both eyes is routed mainly to the right occipital cortex • Information from the right visual field is routed mainly to the left occipital cortex • Partial crossing at the optic chiasm organizes information by visual field rather than by eye • Slides 14-15.

What are retinotopic organization, cortical blindness and a scotoma?

• Retinotopic organization: neighbouring retinal locations map onto neighbouring areas of visual cortex • Occipital damage can cause cortical blindness despite intact eyes • Focal damage can create a scotoma, a pathological blind region corresponding to the damaged map • A scotoma differs from the normal optic-disc blind spot • Slide 15.

What causes cerebral achromatopsia, and how does it differ from cone-based colorblindness?

• Damage to area V4 in occipital cortex produces loss of color perception despite functioning eyes and cones • The world may appear grayscale, and color imagery or dreams can also be affected • Food and other stimuli may become less motivating • Cone-based colorblindness begins in retinal photoreceptors and usually impairs selected color distinctions rather than eliminating cortical color experience • Slide 16.

What causes cerebral akinetopsia, and what would the person experience?

• Damage to area V5 in occipital cortex disrupts motion perception • Moving objects appear as disconnected snapshots or strobe-light-like flashes rather than smooth trajectories • Tasks such as pouring a drink, crossing a road or judging speed become difficult even though object and color vision may remain • Slide 17.

Match sound-wave properties to auditory perception.

• Frequency: pitch; higher frequency produces higher pitch • Amplitude: loudness; greater amplitude produces louder sound • Complexity: timbre; mixtures of frequencies distinguish sounds even when pitch and loudness are similar • Slide 18.

Identify the main structures of the auditory system and their roles.

• Pinna and auditory canal collect and funnel sound • Tympanic membrane vibrates • Ossicles transmit and amplify vibration • Cochlea contains fluid, basilar membrane and hair cells for transduction • Auditory nerve carries neural signals to the brain • Semicircular canals support balance rather than hearing • Slide 19.

Give the ordered sequence of auditory transduction.

• Pinna directs pressure waves into auditory canal • Tympanic membrane vibrates • Ossicles amplify and transmit vibration to the inner ear • Cochlear fluid moves the basilar membrane • Hair-cell cilia bend and convert mechanical energy into neural signals • Auditory nerve carries output toward the brain • Slides 19-20.

How does the cochlea represent different sound frequencies?

• Different frequencies produce maximum movement at different places along the basilar membrane • Hair cells at those locations are tuned to particular frequency ranges • The brain infers pitch partly from which hair-cell populations and auditory pathways are activated • Slides 20-22.

Distinguish conductive from sensorineural hearing loss.

• Conductive loss: sound transmission is blocked or weakened in the outer or middle ear before reaching the cochlea • Sensorineural loss: cochlear hair cells, cilia or the auditory nerve are damaged • Conductive problems may be mechanically treatable; sensorineural damage is often more permanent • Slide 21.

Match ear-wax buildup, ruptured tympanic membrane and otosclerosis to their hearing effects.

• Ear wax blocks the auditory canal • A ruptured tympanic membrane cannot transmit vibration normally, although it may heal • Otosclerosis fuses or immobilizes ossicles so they cannot amplify and pass vibrations efficiently • All are examples of conductive hearing loss • Slide 21.

How can hair-cell damage cause frequency-specific hearing loss?

• Hair cells at different cochlear locations respond best to different frequencies • Damage to a particular region removes sensitivity for its frequency range • Auditory-nerve damage can impair signal transmission more broadly • These are sensorineural rather than conductive deficits • Slide 21.

How is sound processed in primary auditory cortex and beyond?

• Area A1 in the temporal lobe is tonotopically organized, so neighbouring regions respond to neighbouring frequencies • Basic auditory features are represented in A1 • More complex information such as speech continues to secondary and specialized temporal-lobe areas • Slide 22.

How does the brain localize a sound using interaural timing?

• A sound from one side reaches the nearer ear slightly earlier than the farther ear • The brain compares this arrival-time difference between the ears • The tectum, especially the inferior colliculus, helps compute interaural timing and infer sound direction • Slide 23.

How does the vestibular system support balance and orientation?

• Fluid-filled semicircular canals respond to head rotation in different planes • Movement of fluid bends vestibular hair cells • Their signals inform the brain about head motion and orientation • The brain combines vestibular, visual and proprioceptive input to maintain balance • Slide 24.

Why does motion sickness occur, and what can reduce it?

• Motion sickness arises when vestibular signals indicate movement but visual signals suggest stillness, or vice versa • Looking outside at the horizon can align visual and vestibular information • Minimizing head movement and some medications can reduce vestibular effects • Aging-related vestibular changes may alter balance and susceptibility • Slide 24.