Under What Circumstances Can Sensory Input Be Registered Without Conscious Awareness?

Chapter 17. Sensory Systems

17.1 Sensory Processes

Learning Objectives

By the end of this department, y'all volition be able to:

Identify the general and special senses in humans
Describe three of import steps in sensory perception
Explain the concept of just-noticeable difference in sensory perception

Senses provide information about the body and its environment. Humans have v special senses: olfaction (smell), gustation (gustation), equilibrium (balance and body position), vision, and hearing. Additionally, we possess general senses, also called somatosensation, which respond to stimuli like temperature, pain, pressure, and vibration. Vestibular sensation, which is an organism's sense of spatial orientation and rest, proprioception (position of bones, joints, and muscles), and the sense of limb position that is used to track kinesthesia (limb motion) are function of somatosensation. Although the sensory systems associated with these senses are very different, all share a common function: to convert a stimulus (such every bit light, or sound, or the position of the trunk) into an electrical signal in the nervous system. This procedure is called sensory transduction.

There are 2 broad types of cellular systems that perform sensory transduction. In one, a neuron works with a sensory receptor, a prison cell, or jail cell process that is specialized to engage with and detect a specific stimulus. Stimulation of the sensory receptor activates the associated afferent neuron, which carries information near the stimulus to the central nervous organisation. In the 2d type of sensory transduction, a sensory nervus ending responds to a stimulus in the internal or external environment: this neuron constitutes the sensory receptor. Complimentary nerve endings can be stimulated by several unlike stimuli, thus showing footling receptor specificity. For example, hurting receptors in your gums and teeth may be stimulated by temperature changes, chemical stimulation, or pressure level.

Reception

The first step in sensation is reception

, which is the activation of sensory receptors by stimuli such as mechanical stimuli (being bent or squished, for example), chemicals, or temperature. The receptor can then reply to the stimuli. The region in space in which a given sensory receptor tin can respond to a stimulus, exist it far away or in contact with the body, is that receptor'due south receptive field. Think for a moment virtually the differences in receptive fields for the different senses. For the sense of touch, a stimulus must come into contact with trunk. For the sense of hearing, a stimulus can be a moderate altitude abroad (some baleen whale sounds can propagate for many kilometers). For vision, a stimulus can be very far abroad; for example, the visual arrangement perceives light from stars at enormous distances.

Transduction

The well-nigh fundamental function of a sensory system is the translation of a sensory betoken to an electrical signal in the nervous organization. This takes place at the sensory receptor, and the alter in electrical potential that is produced is called the receptor potential. How is sensory input, such as force per unit area on the skin, changed to a receptor potential? In this example, a type of receptor called a mechanoreceptor (as shown in

Figure 17.2) possesses specialized membranes that reply to pressure level. Disturbance of these dendrites past compressing them or angle them opens gated ion channels in the plasma membrane of the sensory neuron, irresolute its electrical potential. Recall that in the nervous system, a positive change of a neuron's electric potential (as well chosen the membrane potential), depolarizes the neuron. Receptor potentials are graded potentials: the magnitude of these graded (receptor) potentials varies with the forcefulness of the stimulus. If the magnitude of depolarization is sufficient (that is, if membrane potential reaches a threshold), the neuron will fire an action potential. In most cases, the right stimulus impinging on a sensory receptor volition bulldoze membrane potential in a positive management, although for some receptors, such every bit those in the visual system, this is non always the instance.

Figure_36_01_01f — Figure 17.2. (a) Mechanosensitive ion channels are gated ion channels that respond to mechanical deformation of the plasma membrane. A mechanosensitive channel is connected to the plasma membrane and the cytoskeleton past hair-similar tethers. When pressure level causes the extracellular matrix to movement, the channel opens, allowing ions to enter or exit the cell. (b) Stereocilia in the human ear are connected to mechanosensitive ion channels. When a sound causes the stereocilia to move, mechanosensitive ion channels transduce the signal to the cochlear nervus.

Sensory receptors for different senses are very different from each other, and they are specialized co-ordinate to the type of stimulus they sense: they have receptor specificity. For example, touch receptors, calorie-free receptors, and sound receptors are each activated by different stimuli. Affect receptors are not sensitive to lite or sound; they are sensitive but to touch or pressure. Nevertheless, stimuli may be combined at higher levels in the brain, as happens with olfaction, contributing to our taste.

Encoding and Manual of Sensory Information

Four aspects of sensory data are encoded by sensory systems: the type of stimulus, the location of the stimulus in the receptive field, the duration of the stimulus, and the relative intensity of the stimulus. Thus, activity potentials transmitted over a sensory receptor'south afferent axons encode one blazon of stimulus, and this segregation of the senses is preserved in other sensory circuits. For example, auditory receptors transmit signals over their own dedicated organization, and electric activity in the axons of the auditory receptors will exist interpreted by the brain equally an auditory stimulus—a sound.

The intensity of a stimulus is often encoded in the rate of activity potentials produced by the sensory receptor. Thus, an intense stimulus will produce a more rapid train of action potentials, and reducing the stimulus will likewise deadening the rate of production of activity potentials. A second way in which intensity is encoded is past the number of receptors activated. An intense stimulus might initiate action potentials in a large number of adjacent receptors, while a less intense stimulus might stimulate fewer receptors. Integration of sensory information begins as soon equally the data is received in the CNS, and the brain volition further process incoming signals.

Perception

Perception is an individual's estimation of a sensation. Although perception relies on the activation of sensory receptors, perception happens not at the level of the sensory receptor, but at higher levels in the nervous organisation, in the brain. The brain distinguishes sensory stimuli through a sensory pathway: activity potentials from sensory receptors travel along neurons that are dedicated to a particular stimulus. These neurons are dedicated to that detail stimulus and synapse with particular neurons in the encephalon or spinal cord.

All sensory signals, except those from the olfactory arrangement, are transmitted though the cardinal nervous organisation and are routed to the thalamus and to the appropriate region of the cortex. Recall that the thalamus is a construction in the forebrain that serves as a clearinghouse and relay station for sensory (as well equally motor) signals. When the sensory point exits the thalamus, information technology is conducted to the specific area of the cortex (Figure 17.3) defended to processing that particular sense.

How are neural signals interpreted? Interpretation of sensory signals between individuals of the same species is largely like, attributable to the inherited similarity of their nervous systems; withal, there are some private differences. A good instance of this is individual tolerances to a painful stimulus, such as dental hurting, which certainly differ.

Figure_36_01_02 — Figure 17.3. In humans, with the exception of olfaction, all sensory signals are routed from the (a) thalamus to (b) terminal processing regions in the cortex of the brain. (credit b: modification of work past Polina Tishina) Scientific Method Connection

Only-Noticeable Difference

Information technology is easy to differentiate between a one-pound handbag of rice and a ii-pound purse of rice. There is a one-pound departure, and one bag is twice as heavy as the other. However, would it be equally easy to differentiate between a 20- and a 21-pound pocketbook?

Question: What is the smallest detectible weight difference between a i-pound pocketbook of rice and a larger bag? What is the smallest detectible deviation between a 20-pound bag and a larger bag? In both cases, at what weights are the differences detected? This smallest detectible deviation in stimuli is known equally the merely-noticeable difference (JND).

Background: Inquiry background literature on JND and on Weber's Law, a description of a proposed mathematical relationship between the overall magnitude of the stimulus and the JND. Yous volition be testing JND of unlike weights of rice in numberless. Choose a user-friendly increment that is to be stepped through while testing. For example, you could cull 10 percent increments between one and two pounds (one.1, i.2, one.3, 1.4, and and then on) or 20 percent increments (i.two, 1.4, 1.six, and 1.8).

Hypothesis: Develop a hypothesis virtually JND in terms of percentage of the whole weight beingness tested (such as "the JND between the 2 small bags and between the two big bags is proportionally the same," or ". . . is non proportionally the same.") So, for the outset hypothesis, if the JND between the 1-pound pocketbook and a larger bag is 0.two pounds (that is, xx percentage; one.0 pound feels the same every bit ane.one pounds, simply 1.0 pound feels less than one.2 pounds), then the JND between the xx-pound purse and a larger pocketbook will also be twenty pct. (And then, twenty pounds feels the same as 22 pounds or 23 pounds, but 20 pounds feels less than 24 pounds.)

Test the hypothesis: Enlist 24 participants, and split up them into two groups of 12. To prepare up the demonstration, assuming a 10 percent increase was selected, have the starting time group exist the one-pound group. As a counter-balancing measure against a systematic error, however, six of the offset group will compare 1 pound to two pounds, and stride down in weight (one.0 to 2.0, one.0 to ane.9, and then on.), while the other six will step up (one.0 to 1.1, ane.0 to 1.2, and then on). Employ the aforementioned principle to the xx-pound group (twenty to forty, 20 to 38, and and so on, and 20 to 22, twenty to 24, and so on). Given the large deviation between 20 and 40 pounds, you may wish to employ xxx pounds as your larger weight. In any case, use two weights that are easily detectable equally dissimilar.

Record the observations: Record the data in a tabular array like to the table below. For the one-pound and xx-pound groups (base weights) tape a plus sign (+) for each participant that detects a departure between the base of operations weight and the footstep weight. Record a minus sign (-) for each participant that finds no difference. If i-tenth steps were non used, and so replace the steps in the "Stride Weight" columns with the step you are using.

Table 17 .1. Results of JND Testing (+ = difference; – = no difference)
Step Weight	Ane pound	20 pounds	Step Weight
ane.i			22
1.2			24
one.3			26
1.4			28
1.five			thirty
1.6			32
1.7			34
1.eight			36
1.9			38
2.0			40

Analyze the data/report the results: What step weight did all participants find to be equal with 1-pound base of operations weight? What well-nigh the xx-pound group?

Draw a conclusion: Did the information support the hypothesis? Are the final weights proportionally the same? If not, why non? Do the findings adhere to Weber's Police force? Weber's Law states that the concept that a just-noticeable difference in a stimulus is proportional to the magnitude of the original stimulus.

Summary

A sensory activation occurs when a physical or chemical stimulus is processed into a neural signal (sensory transduction) by a sensory receptor. Perception is an individual estimation of a sensation and is a brain function. Humans have special senses: olfaction, gustation, equilibrium, and hearing, plus the general senses of somatosensation.

Sensory receptors are either specialized cells associated with sensory neurons or the specialized ends of sensory neurons that are a part of the peripheral nervous system, and they are used to receive information nearly the surroundings (internal or external). Each sensory receptor is modified for the type of stimulus it detects. For example, neither gustatory receptors nor auditory receptors are sensitive to light. Each sensory receptor is responsive to stimuli within a specific region in space, which is known every bit that receptor's receptive field. The almost fundamental function of a sensory system is the translation of a sensory signal to an electrical signal in the nervous system.

All sensory signals, except those from the olfactory organisation, enter the key nervous organization and are routed to the thalamus. When the sensory signal exits the thalamus, it is conducted to the specific area of the cortex dedicated to processing that detail sense.

Exercises

Which of the following statements about mechanoreceptors is false?
1. Pacini corpuscles are found in both glabrous and hairy skin.
2. Merkel'southward disks are arable on the fingertips and lips.
3. Ruffini endings are encapsulated mechanoreceptors.
4. Meissner's corpuscles extend into the lower dermis.
Where does perception occur?
1. spinal cord
2. cerebral cortex
3. receptors
4. thalamus
If a person's cold receptors no longer convert cold stimuli into sensory signals, that person has a problem with the procedure of ________.
1. reception
2. manual
3. perception
4. transduction
After somatosensory transduction, the sensory indicate travels through the brain as a(n) _____ signal.
1. electrical
2. force per unit area
3. optical
4. thermal

Answers

Glossary

kinesthesia: sense of body move
mechanoreceptor: sensory receptor modified to respond to mechanical disturbance such equally beingness bent, touch, pressure level, motion, and audio
perception: individual estimation of a awareness; a encephalon function
proprioception: sense of limb position; used to rail faculty
reception: receipt of a signal (such as calorie-free or audio) past sensory receptors
receptive field: region in space in which a stimulus can activate a given sensory receptor
receptor potential: membrane potential in a sensory receptor in response to detection of a stimulus
sensory receptor: specialized neuron or other cells associated with a neuron that is modified to receive specific sensory input
sensory transduction: conversion of a sensory stimulus into electrical free energy in the nervous system by a change in the membrane potential
vestibular sense: sense of spatial orientation and balance