Answers to Concept Checks

• 2.1
  1. Sensory receptor → afferent neuron → sensory ganglion → spinal cord → brain (projection areas)
  2. 1–F, 2–A, 3–E, 4–D, 5–C, 6–G, 7–B
  3. Absolute threshold is the minimum stimulus that can evoke an action potential in a sensory receptor. Threshold of conscious perception is the minimum stimulus that can evoke enough action potentials for a long enough time that the brain perceives the stimulus. The difference threshold (just-noticeable difference) is the minimum difference between two stimuli that can be detected by the brain.
  4. Weber’s law explains that just-noticeable differences are best expressed as a ratio, which is constant over most of the range of sensory stimuli. Signal detection theory concerns the threshold to sense a stimulus, given obscuring internal and external stimuli.
  5. Adaptation generally raises the difference threshold for a sensory response; as one becomes used to small fluctuations in the stimulus, the difference in stimulus required to evoke a response must be larger.
• 2.2
  1. Cornea: gathers and focuses the incoming light
     Pupil: allows passage of light from the anterior to posterior chamber
     Iris: controls the size of the pupil
     Ciliary body: produces aqueous humor; accommodation of the lens
     Canal of Schlemm: drains aqueous humor
     Lens: refracts the incoming light to focus it on the retina
     Retina: detects images
     Sclera: provides structural support
  2. Cornea → pupil → lens → vitreous → retina (rods and cones → bipolar cells → ganglion cells) → optic nerve → optic chiasm → optic tract → lateral geniculate nucleus (LGN) of thalamus → radiations through parietal and temporal lobes → visual cortex (occipital lobe)
  3. Parallel processing is the ability to simultaneously analyze color, shape, and motion of an object and to integrate this information to create a cohesive image of the world. Parallel processing also calls on memory systems to compare a visual stimulus to past experiences to help determine the object’s identity.
  4. Cones are responsible for color. Parvocellular cells are responsible for shape. Magnocellular cells are responsible for motion.
• 2.3
  1. Linear acceleration is detected by the utricle and saccule. Rotational acceleration is detected by the semicircular canals.
  2. Pinna → external auditory canal → tympanic membrane → malleus → incus → stapes → oval window → perilymph in cochlea → basilar membrane → hair cells → vestibulocochlear nerve → brainstem → medial geniculate nucleus (MGN) of thalamus → auditory cortex (temporal lobe)
  3. The basilar membrane is tonotopically organized: high-pitched sounds cause vibrations at the base of the cochlea, whereas low-pitched sounds cause vibrations at the apex of the cochlea.
• 2.4
  1. Nostril → nasal cavity → olfactory chemoreceptors (olfactory nerves) on olfactory epithelium → olfactory bulb → olfactory tract → higher-order brain regions, including limbic system
  2. Smell is sensitive to volatile or aerosolized compounds; taste is sensitive to dissolved compounds.
  3. The four main modalities of somatosensation are pressure, vibration, pain, and temperature.
• 2.5
  1. Bottom-up processing requires each component of an object to be interpreted through parallel processing, and then integrated into one cohesive whole. Top-down processing starts with the whole object and, through memory, creates expectations for the components of the object.
     
     

  2. Gestalt Principle	Description
     Proximity	Components close to one another tend to be perceived as a unit.
     Similarity	Components that are similar (in color, shape, size) tend to be grouped together.
     Good continuation	Components that appear to follow in the same pathway tend to be grouped together; abrupt changes in form are less likely than continuation of the same pattern.
     Subjective contours	Edges or shapes that are not actually present can be implied by the surrounding objects (especially if good continuation is present).
     Closure	A space enclosed by a contour tends to be perceived as a complete figure; such figures tend to be perceived as more complete (or closed) than they really are.
     Prägnanz	Perceptual organization will always be as regular, simple, and symmetric as possible.