Sensory Integration Minute – Broken Escalator

Broken Escalator

Some of you listening tonight may have experienced the ’broken escalator phenomenon’, namely the sensation that when walking onto an escalator that is stationary, you experienced an odd sensation of imbalance, despite the knowledge that the escalator wasn’t going to move. This is a particularly interesting phenomenon because it represents a rare example of the dissociation between knowledge of the world and subsequent action. A couple of professors at the Imperial College of London, Drs. Reynolds and Bronstein, have investigated this phenomenon. They first had people walk down a short walkway, step on a stationary platform that was embedded into the floor and then keep walking. During the experiments they measured walking velocity. Next they had people practice walking onto the same platform only this time the platform was moving. The platform moved forward just like an escalator does. During their initial experiments, they had the subjects practice walking onto the moving platform 20 times and then told them that during the next set of trials the platform would no longer be moving. Consistent with the broken elevator phenomenon, the subjects approached the platform at a higher walking velocity than when they had previously practiced without the platform moving. This resulted in a large overshoot of their trunk such that they swayed forward with many subjects being forced to reach out and grab a handrail to keep from falling. Aftereffects such as this one are occasionally seen in movement-related experiments after subjects practice a large number of trials in a certain condition and then move to a new condition.

What is interesting about this particular phenomenon is that the professors redid the experiment but this time they provided the subjects only one practice trial in which the platform was moving. Nonetheless, when they told the subjects that during the next trial the platform would not be moving, the subjects still displayed the inappropriate behavior, again resulting in a large overshoot and loss of balance. This broken escalator phenomenon is an interesting example of how accurate sensory information and knowledge can be ignored by the central nervous system and lead to dangerous situations.

Sensory Integration Minute – Phone Use in Cars

Phone Use in Cars

Have you ever finally been able to pass an erratic driver on the road and said ‘well that’s no surprise, they are on the phone’ as a way of explaining that person’s poor driving? Not surprisingly, there have been a number of research studies investigating the impact of cell phone use while driving. Interestingly Dr. I.D. Brown and colleagues brought up the concerns about phone use and driving back in 1969, (as an aside, Dr. Brown must have been watching James Bond movies at that time to learn that phones were about to become a regular feature in cars). Dr. Brown’s concerns weren’t so much about having your hands free to operate the phone, (he didn’t anticipate the invention of the cell phone) but rather he worried about the attention required to both speak over the phone and drive at the same time. As was stated in the 1969 research article ‘A more important and lasting problem arises from the hypothesis that man can be considered to act as a single communication channel of limited capacity. The prediction from this hypothesis is that the driver will often be able to telephone only by switching attention between the informational demands of the two tasks. Telephoning could thus interfere with driving by disrupting visual scanning, since visual and auditory information would have to be transmitted successively. It could also interfere by overloading short term memory and impairing judgment of relative velocity.

More current research has shown that being on the phone will driving does tax the attentional system and provides a scientific explanation for why it is difficult to integrate multiple sources of sensory information while driving and talking on the phone.

Sensory Integration Minute – Two Visual Systems

Two Visual Systems

When you look at an object, say the book you are using to study, and when you walk through an unfamiliar classroom, were you aware you are relying of two different visual systems to accomplish those two tasks? That’s right; research has demonstrated that we have two relatively distinct visual systems. Your focal or central visual system is primarily used to identify objects and relies heavily on the fovea of the eye where acuity is high. Identifying objects requires conscious thought and the information transmitted by your central visual system terminates in your visual cortex. Some diseases of your visual cortex may not lead to blindness in the traditional sense but would prevent from identifying the objects you are seeing. The relatively common age-related macular degeneration primarily affects your central vision.

In contrast, your ambient system is used for detecting space around your body and locating where objects are around you. You can think of this as your peripheral visual system and it relies on sensory input from the entire retina. Because you ambient system uses input from the entire retina it’s functioning is not degraded anywhere near to the degree your focal system is in low light. It is this system that enables us to walk through a cluttered room at night without stubbing our toes. Evidence supporting the existence of an ambient visual system comes from studies with patients who had damage to their visual cortex which caused blindness in parts of their visual field. These patients were unable to identify objects in this part of their visual field because, as they reported they ‘couldn’t see’ the object. However, when then were asked to identify where the object was, they had no trouble pointing to the object, strongly suggesting that we do, in fact, have two visual systems we us to integrate visual sensory information

Sensory Integration Minute – Security Margin

Security Margin

Previously we have discussed the physical space that surrounds a person and labeled it peripersonal space or near space. Not surprisingly, there is evidence that suggests we interact with the external world by adopting a security margin: a distance between ourselves and the environment that dictates our response to the environment. For example, it has been shown that people walking through a doorway rotate their shoulders at a fixed ratio of doorway width to shoulder width. That is, if the door way is wide, people don’t rotate their shoulders to pass through the doorway but as the doorway narrows people will rotate their shoulders even if the doorway remains wide enough to pass through without shoulder rotation. All people, regardless of their shoulder width, rotate their shoulders at the same ratio of one point three. In other words, a large American football player and a small gymnast’s behavior will be dictated in the same way when confronted with a proportionally sized doorway. This security margin clearly provides room for error in avoidance of the doorway should one slightly misstep while passing through the doorway. Perhaps, most interestingly, is that this security margin is an unconscious response to the environment and represents a great example of the symbiotic relationship between our ability to integrate sensory information from the environment and our behavior.

Ahh, but we will leave human asymmetries for another day.

Sensory Integration Minute – Self Simulation

Self Stimulation

It is well documented that a significant number of individuals with mental retardation practice self-stimulating, and in some cases, self-injurous behaviors. Self-stimulating behaviors are repetitive body movements which serves no apparent purpose in the external environment. Two somewhat complimentary theories have been proposed to help explain self stimulation: one is that the behaviors are self reinforcing by providing sensory input not achieved through more conventional behavior, and the second theory suggests that self stimulation is used to regulate sensory information in individuals with sensory processing deficits. Interestingly, self stimulation consists of behaviors that tend to activate the tactile, vestibular, and proprioceptive sensory systems as opposed to the visual and auditory systems. The tactile, vestibular, and proprioceptive systems are important for movement control so it’s no wonder that self stimulating stereotypical behaviors significantly decrease when walking or when purposeful engagement with the external environment occurs. This is another example of how processing of sensory integration is tied to intentional action.

Sensory Integration Minute – Cocktail Party Phenomenon

Cocktail Party Phenomenon

Have you ever been involved in a conversation in a public place with lots of people talking all around you when suddenly you hear your name spoken by someone on the other side of the room? Have you ever wondered how it is that you could attend to your name being spoken but didn’t hear anything else that same speaker was saying? If so, you have experienced the cocktail party phenomenon; the ability to integrate and attend to a single, relevant sound among a variety of competing sounds. Obviously humans have had this perceptual ability for thousands of years. However, the need to formally investigate the cocktail party phenomenon grew acute with the development of commercial planes as a common public transportation mode. What does the growth of commercial flying and the cocktail party phenomenon have to do with each other you ask? Well, in the early 1950’s air traffic controllers received messages from pilots from a single loudspeaker in the control tower. Needless to say, keeping track of whose voice belonged to what pilot, and by extension what plane, was exceedingly difficult. It wasn’t long before researchers were able to figure out that our ability to separate and attend to unique sounds is facilitated by the fact we have two ears that in some intricate ways have the ability to function somewhat independently. A practical result of this finding was that additional loudspeakers were placed in the control tower.

Additional research over the years has revealed that if different sounds reach our ears from different directions in different phases, then our ability to selectively attend to multiple sounds is improved. This finding helps explain the cocktail party phenomenon and is another example of our amazing sensory integration abilities.

Sensory Integration Minute – Sole Vibration

Sole Vibration

We rely on mechanoreceptors in the soles of our feet to provide us information about how we are controlling upright posture. As we sway back and forth while standing these sensory receptors are mechanically stimulated by the interaction between the ground and our soles.

As we age, the cellular processes that enable our sensory systems to transmit the information they are designed to transmit do not functional as well as when we are younger. In the case of our sole receptors, this loss of functionality leads to less postural control and possibly falling. However, researchers have discovered that if you apply a randomly generated vibration to the soles this vibration results in improved postural control and decreases the chances of falling.

The explanation is that vibration functions to engage the sensory receptors on your soles so that they are better able to transmit the information about the interactions between your soles and the ground. You can loosely think of the vibration acting sort of like a warm up so when it is time to perform the activity, the system is in a better position to perform.

The most interesting part of this phenomenon is that for vibration to have a positive impact on posture control, the vibration doesn’t even need to be consciously detected. In other words, people have no idea their feet are being stimulated, but yet, the stimulation is working to improve their postural control. Another great example of how sensory information can be integrated for our benefit.

Sensory Integration Minute – Peripersonal Space

Peripersonal Space

Physical space that surrounds a person is called peripersonal space or near space. The perception of near space can be influenced by a number of variables that often don’t correspond to physical reality. For instance, right handed people perceive their right hands to be larger than their left hands and therefore estimate they can grasp larger objects with their right hands. Similarly, right handed people perceive their right arm to be longer than their left arm and therefore estimate they can reach farther with their right versus left arm.

The perception of the size of near space can be influenced by the size of the body. If people are asked to hold a baton in their hand, the distance to an object is perceived as shorter than when they didn’t hold the baton. What’s interesting about this finding, however, is people only perceive the distance being shorter if they actually intend to reach toward an object in near space. Thus, the way we integrate sensory information and thereby perceive the dimensions of our body and the near space around us is influenced by our intention to act. A clear example of the symbiotic relationship exists between our sensory and action systems.

Sensory Integration Minute – Time to Contact

Time to Contact

Have you ever sat by a body of water and watched birds dive for fish? During flight their wings are open to control position. However, when their wings contact the water their wings must be closed to avoid serious injury. These birds close their wings at a constant time before they contact the water. This means that they must be able to account for the velocity of their dives from different heights. In other words, they can accurately estimate their time to contact with water and use that information to guide their actions. In this case, close their wings.

The scientific variable we use to estimate time to contact is known as TAU and can be thought of the faster an approaching object fills the visual field, the faster you will contact a particular point in space. We use an estimation of the time to contact to conduct a variety of actions. Every time we drive we are constantly estimating our time to contact with the cars in front of us and adjust our actions accordingly. Every time we catch a ball, bring a fork to our mouth, or walk in a crowd, we need information about time to contact to guide our actions. Sometimes we are interested in making contact such as when catching a ball and sometimes our goal is to avoid making contact. Either way, some scientists believe we use TAU to estimate time to contact and it provides us another great example of sensory integration.

Sensory Integration Minute – Detecting Walking

Detecting Walking

Have you ever experienced sitting in an office and someone walks down the hallway and you are able to identify who that person is just from the sound of their footsteps? What you are hearing is the spectrotemporal footprint composed of sound waves that have frequency components. Research has shown that people can identify the gender of complete strangers with up to 70% accuracy based on the sound of their footsteps alone. People can more accurately identify people whom they spend more time around and the longer they hear the footfall pattern the more accurate is the ability to identify that person.

Last week we discussed invariant patterns in the flow of sensory information we receive. It is the invariants in the sound frequency pattern that can be detected despite changes in shoes and floor surfaces.

Each person’s spectrotemporal footprint is as unique as their finger print because it is a product of the confluence of an individual’s anatomy, their nervous system that controls their gait, and their personality that influences their walking pattern. Not surprisingly our human sensory integration system is finely tuned to detect and identify these auditory footprints.

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