4.4—touch and the chemical senses

Question 1

Synesthesia

Answer 1

• people with synesthesia experience blended perceptions, such that affected indiviuals might actually hear colours or feel sounds.
• there’s no clear answer as to why synesthesia occurs.
• brains of people with synesthesia may contain networks that link different sensory areas in ways not found in other people.

Question 2

The Sense of Touch

Answer 2

• we combine information from our different senses into multimodal experiences, such as when taste and smell are combined to create a perception of flavour.
• the touch receptors send information to the somatosensory cortex in the parietal lobes of the brain, the neural region associated with your sense of touch.
• one method of testing sensitivity (acuity) is using the two-point treshhold test.
  
  • regions with high acquity, such as the fingertips, can detect the two separate, but closely spaced pressure points of the device, whereas less sensitive regions such as the lower back will perceive the same stimuli as only one pressure point.

Question 3

Haptics

Answer 3

• haptics: the active, explatory aspect of touch sensation and perception.
• like vision and hearing, touch is very sensitive to change. merely laying your hand on the surface of an object does little to help identify it.
• haptics allows us not only to identify objects, but also to avoid damaging or dropping them.

Question 4

Kinesthesis

Answer 4

• kinesthesis: the sense of bodily motion and position.
• receptors for kinesthesis reside in the muscles, joints, and tendons.
• they transmit information about movement and the position of your muscles, limbs, and joints to the brain.

Question 5

Nociception

Answer 5

• nociception: the activity of nerve pathways that respond to uncomfortable stimulation.
• our skin, teeth, corneas, and internal organs contain nerve endings called nocieptors, which are receptors that initiate pain messages that travel to the central nervous system.
• fast fibres register sharp, immediate pain.
• slow fibres register chronic, dull pain.
• these impulses first travel to the spinal cord.

Question 6

Gate-Control Theory

Answer 6

• gate-control theory: which explains our experience of pain as an interaction between nerves that transmit pain messages and those that inhibit these messages.
• cells in the spinal cord regulate how much pain signalling reaches the brain.
• small nerve fibres that conduct pain messages and larger neve fibres that conduct other sensory signals.
• the somatosensory cortex, registers the pain sensations occuring over the entire surface of the body.
• the anterior cingulate gyrus, influences our attentional and emotional responses to the pain; this brain region is found on the medial (middle) surface of the brain immediately above the corpus callosum.

Question 7

Phantom Limb Sensations

Answer 7

• phantom limb sensations: are frequently experienced by amputees, who report pain and other sensations coming from the absent limb.
• after limb amputation, the area of the somatosensory cortex formerly associated with that area is no longer stimulated by the lost limb.
• healthy nerve cells become hypersensitive when they lose connections. the phantom sensations, including pain, may occur because the nerve cells in the cortex continue to be active, despite the absence of any input from the body.
• the mirror box—amputees often find that watching themselves move and stretch the phantom hand, which is actually the mirror image of the real hand, results in a significant decrease in phantom pain and in both physical and emotional discomfort.

Question 8

Gustatory System

Answer 8

• gustatory system: functions in the sensation and perception of taste.
• primary tastes: salty, sweet, bitter, and sour.
  
  • a fifth taste, called umami, is a Japanese word that refers to tastes associated with seaweed, MSG, and protein-rich foods such as milk and aged cheese.
• Our experience of taste reflects an overall pattern of activity across many neurons, and generally comes from stimulation of the entire tongue rather than just specific, localized regions.
• The middle of the tongue has very few taste receptors, giving it a similar character to the blind spot on the retina.
• papillae: small bumps on the surface of the tongue where the receptors for taste are located.
• the bundles of nerves that register taste at the taste buds send the signal through the thalamus and on to high-level regions of the brain.
• gustatory cortex: located in the back of the frontal lobes and extends inward to the insula (near the top of the temporal lobe).
• secondary gustatory cortex: processes the pleasurable experiences associated with food.
• supertasters; account for 25% of the population and are especially sensitive ot bitter tastes such as those of broccoli and black coffee.

Question 9

Olfactory System

Answer 9

involved in smell—the detection of airborne particles with specialized receptors located in the nose.

Question 10

Olfactory Epithelium

Answer 10

a thin layer of cells that are lined by the sensory receptors called cilia (tiny hair-like projections that contain specialized proteins that bind with the airborne molecules that enter the nasal cavity.

Question 11

The Olfactory System

Answer 11

• Humans have roughly 1000 different types of odour receptors in their olfactory system.
• If this is the case, then how it is possible for us to detect approximately 10 000 different smells?
• pattern of the stimulation, involving more than one receptor, which gives rise to the experience of a particular smell
• Different combinations of cilia are stimulated in response to different odours.
• These groups of cilia then transmit messages to neurons that converge on the olfactory bulb (on the bottom surface of the frontal lobes)
  
  • olfactory bulb connects with several regions of the brain through the olfactory tract, including the limbic system (emotion) as well as regions of the cortex where the subjective experience of pleasure (or disgust) occurs.

Question 12

Multimodal Integration

Answer 12

the ability to combine sensation from different modalities such as vision and hearing into a single integrated perception.

Question 13

McGurk Effect

Answer 13

• McGurk Effect: when someone’s expectations bias the perception of presented sounds.
• when the sound “ba-ba” was presented during a video of someone mouthing “ga-ga”, people perceived it as “da-da”.