What is the lowest level of stimulation?

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The following list offers general suggestions for family, friends, and staff to reduce overstimulation. Please talk to your team members for more specific suggestions to implement with your family member.

Keep lights dim or limit the number of lights that are used.
Keep the door to the room closed and pull the curtain around the bed (if shared room).
Encourage and allow frequent rest periods.
Limit the amount of time the television or radio is turned on. Keep the volume low. Consider the “care channel” as a choice for the TV channel. Turn the TV or radio off when visitors are present.
Limit the number of visitors in the room (usually no more than 2). Speak one at a time. Keep visits short.
Always identify yourself when entering the room.
Use a calm voice and speak slowly.
Conversations in the room should be directed towards the patient. If the patient is not involved in the conversation step out of the room.
Consider the amount of visual stimulation in the room (number of pictures, banners) etc.

**Remember, the brain is working when it is processing information of any kind. Don’t “over work” the brain by giving too much to process at any given time.

Signs of Over-stimulation After a brain injury, your family member requires extra work to process and make sense out of their environment. If there is too much input or “stimulation” for them to deal with they may become “overstimulated” resulting in less than optimal functioning.

Signs of Over-stimulation

Increased restlessness, as in increased movement or pacing
Increased stiffening of the muscles
Increased moaning or crying out
Facial grimacing
Blood pressure and pulse rate changes (not easily observed)
Shutting down or closing off. A person may close eyes, turn away and be very calm. This is one of the later signs of over-stimulation and is just as important to detect.
Increased agitation, yelling, or anger
Increased confusion or just not performing at their “best”
Increased pulling at tubes, clothing, etc.

If you observe any of these symptoms, use the “low stimulation” guidelines for creating an optimal environment. Please don’t hesitate to ask your team members for help with re-establishing the best surroundings.

Activities to do with Your Family Member

The following are some general suggestions - please speak with your team members to establish other appropriate activities.

Give simple and repeated directions when you ask the patient to do something. It may take longer for the patient to understand what he/she hears, so allow extra time to respond before repeating information.
Use firm gentle touch.
Treat your family member appropriately; speak to him/her as you did before the injury. Tell them that something is going to happen before it actually does (combing hair, moving patient, etc.)
Call person by name and repeat orientation information with them. Talk about where the patient is; date; day; why patient is in the hospital; how long they have been there, and about special interests, family members, and friends.
Do NOT quiz the patient – asking them the date, time, etc... Give them the correct information in conversation without quizzing them.
Patient’s favorite scents can be used to provide olfactory stimulation (sense of smell). You can use lotions or perfumes but remember that heavy constant scents can be over-stimulating.
Family pictures are helpful for visual stimulation. Please bring pictures of family with description and therapy staff can arrange pictures so not to be over stimulating.
Remember that it is OK to just sit with your family without conversation.
Feel free to read to your family member, touch patient, and reassure him/her. Do what is comfortable and normal in your interaction.
Always consider the possibility of overstimulation and be aware of signs of “overstimulation”

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Revised: 1/2015

This resource is provided as a courtesy of Craig Hospital. For more information, contact the Craig Hospital Nurse Advice Line at 1-800-247-0257.

Disclaimer: The content in this document is intended for general informational purposes only and is not a substitute for professional medical advice or treatment for specific medical conditions. No professional relationship is implied or otherwise established by reading this document. You should not use this information to diagnose or treat a health problem or disease without consulting with a qualified healthcare provider. Many of the resources references are not affiliated with Craig Hospital. Craig Hospital assumes no liability for any third party material or for any action or inaction taken as a result of any content or any suggestions made in this document and should not be relied upon without independent investigation. The information on this page is a public service provided by Craig Hospital and in no way represents a recommendation or endorsement by Craig Hospital.

In psychophysics, sensory threshold is the weakest stimulus that an organism can sense. Unless otherwise indicated, it is usually defined as the weakest stimulus that can be detected half the time, for example, as indicated by a point on a probability curve.[1] Methods have been developed to measure thresholds in any of the senses.

Several different sensory thresholds have been defined;[2]

Absolute threshold: the lowest level at which a stimulus can be detected.
Recognition threshold: the level at which a stimulus can not only be detected but also recognised.
Differential threshold: the level at which an increase in a detected stimulus can be perceived.
Terminal threshold: the level beyond which a stimulus is no longer detected.

The first systematic studies to determine sensory thresholds were conducted by Ernst Heinrich Weber, a physiologist and pioneer of experimental psychology at the Leipzig University.[3] His experiments were intended to determine the absolute and difference, or differential, thresholds. Weber was able to define absolute and difference threshold statistically which led to the establishment of Weber's Law and the concept of just noticeable difference to describe threshold perception of stimuli.

Following Weber's work, Gustav Fechner, a pioneer of psychophysics, studied the relationship between the physical intensity of a stimulus and the psychologically perceived intensity of the stimulus.[4] Comparing the measured intensity of sound waves with the perceived loudness, Fechner concluded that the intensity of a stimulus changes in proportion to the logarithm of the stimulus intensity. His findings would lead to the creation of the decibel scale.[3]

Defining and measuring sensory thresholds requires setting the sensitivity limit such that the perception observations lead to the absolute threshold. The level of sensitivity is usually assumed to be constant in determining the threshold limit. There are three common methods used to determine sensory thresholds:[2]

Method of Limits: In the first step, the subject is stimulated by strong, easily detectable stimuli that are decreased stepwise (descending sequence) until they cannot detect the stimulus. Then another stimulation sequence is applied called ascending sequence. In this sequence, stimulus intensity increases from subthreshold to easily detectable. Both sequences are repeated several times. This yields several momentary threshold values. In the following step, mean values are calculated for ascending and descending sequences separately. The mean value will be lower for descending sequences. In case of audiometry, the difference of the means in case of ascending vs. descending sequences has a diagnostic importance. In the final step, average of the previously calculated means will result the absolute threshold.
Method of constant stimuli: Stimuli of varying intensities are presented in random order to a subject. Intensities involve stimuli which are surely subthreshold and stimuli which are surely supra-threshold. For the creation of the series, the approximate threshold judged by a simpler method (i.e.: by the method of limits). The random sequences are presented to the subject several times. The strength of the stimulus, perceived in more than half of the presentations will be taken as the threshold.
Adaptive method: Stimulation starts with a surely supra-threshold stimulus; then further stimuli are given with an intensity decreased in previously-defined steps. The series is stopped when the stimulus strength become subthreshold (this is called the turn phenomena). Then the step is halved and the stimulation is repeated, but now with increasing intensities, until the subject perceives the sound again. This process is repeated several times, until the step size reaches the preset minimal value. With this method, the threshold value can be delineated very accurately. The initial size of the step can be selected depending on the expected accuracy.

In measuring sensory threshold, noise must be accounted for. Signal noise is defined as the presence of extra, unwanted energy in the observational system which obscures the information of interest. As the measurements come closer to the absolute threshold, the variability of the noise increases causing the threshold to be obscured.[5] Different types of internal and external noise include excess stimuli, nervous system over- or under-stimulation,[6] and conditions that falsely stimulate nerves in the absence of external stimuli.

A universal absolute threshold is difficult to define a standard because of the variability of the measurements.[7] While sensation occurs at the physical nerves, there can be reasons why it is not consistent. Age[8] or nerve damage can affect sensation. Similarly, psychological factors can affect perception of physical sensation. Mental state, memory,[9] mental illness,[10] fatigue, and other factors can alter perception.

When related to motion in any of the possible six degrees of freedom (6-DoF), the fact that sensory thresholds exist is why it is essential that aircraft have blind-flying instruments. Sustained flight in cloud is not possible by `seat-of-the-pants' cues alone since errors build up due to aircraft movements below the pilot's sensory threshold, ultimately leading to loss of control.

In flight simulators with motion platforms, the motion sensory thresholds are utilised in the technique known as `acceleration-onset cueing'. This is where a motion platform, having made the initial acceleration that is sensed by the simulator crew, the platform is re-set to approximately its neutral position by being moved at a rate below the sensory threshold and is then ready to respond to the next acceleration demanded by the simulator computer.

Detection theory
Odor detection threshold
Perception
Sensory analysis

^ Smith, Christopher U. M. (20 November 2008). Biology of Sensory Systems. John Wiley & Sons. pp. 34–5. ISBN 978-0-470-69438-1. Retrieved 11 October 2014.
^ a b "Determination of sensory thresholds". ttktamop.elte.hu. Retrieved 2016-12-02.
^ a b "Sensation: Thresholds and Psychophysics". users.ipfw.edu. Retrieved 2016-12-02.
^ Swets, John A. (1961-07-21). "Is There a Sensory Threshold?". Science. 134 (3473): 168–177. doi:10.1126/science.134.3473.168. ISSN 0036-8075. PMID 13774294.
^ Cohn, Theodore E; Lasley, D J (1986). "Visual sensitivity". Annual Review of Psychology. 37: 495–521. doi:10.1146/annurev.ps.37.020186.002431. ISSN 0066-4308. PMID 3963783.
^ "Sensory Processing - Introduction to Concepts". classes.kumc.edu. Retrieved 2016-12-02.
^ Meddis, Ray; Lecluyse, Wendy (2011). "The psychophysics of absolute threshold and signal duration: A probabilistic approach" (PDF). Journal of the Acoustical Society of America. 129 (5): 3153–3165. doi:10.1121/1.3569712. ISSN 0001-4966.
^ Humes, Larry E; Busey, Thomas A; Craig; Kewley-Port (1009). "The effects of age on sensory thresholds and temporal gap detection in hearing, vision, and touch". Attention, Perception, & Psychophysics. 71 (4): 860–871. doi:10.3758/APP.71.4.860. ISSN 1943-3921. PMC 2826883. PMID 19429964.
^ Thurgood, Clementine; Whitfield, T W A; Patterson (2011). "Towards a visual recognition threshold: New instrument shows humans identify animals with only 1 ms of visual exposure". Vision Research. 51 (17): 1966–1971. doi:10.1016/j.visres.2011.07.008. ISSN 0042-6989.
^ Adler, Georg; Gattaz, Wagner F (1993). "Pain perception threshold in major depression". Biological Psychiatry. 34 (10): 687–689. doi:10.1016/0006-3223(93)90041-B.