Perception is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment.
An illusion is a distortion of the senses, which can reveal how the human brain normally organizes and interprets sensory stimulation. Although illusions distort our perception of reality, they are generally shared by most people.
Haptic technology, also known as kinaesthetic communication or 3D touch, refers to any technology that can create an experience of touch by applying forces, vibrations, or motions to the user. These technologies can be used to create virtual objects in a computer simulation, to control virtual objects, and to enhance remote control of machines and devices (telerobotics). Haptic devices may incorporate tactile sensors that measure forces exerted by the user on the interface. The word haptic, from the Greek: ἁπτικός (haptikos), means "tactile, pertaining to the sense of touch". Simple haptic devices are common in the form of game controllers, joysticks, and steering wheels.
Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, are sent to the central nervous system.
Multisensory integration, also known as multimodal integration, is the study of how information from the different sensory modalities may be integrated by the nervous system. A coherent representation of objects combining modalities enables animals to have meaningful perceptual experiences. Indeed, multisensory integration is central to adaptive behavior because it allows animals to perceive a world of coherent perceptual entities. Multisensory integration also deals with how different sensory modalities interact with one another and alter each other's processing.
Sensory substitution is a change of the characteristics of one sensory modality into stimuli of another sensory modality.
The kappa effect or perceptual time dilation is a temporal perceptual illusion that can arise when observers judge the elapsed time between sensory stimuli applied sequentially at different locations. In perceiving a sequence of consecutive stimuli, subjects tend to overestimate the elapsed time between two successive stimuli when the distance between the stimuli is sufficiently large, and to underestimate the elapsed time when the distance is sufficiently small.
The tau effect is a spatial perceptual illusion that arises when observers judge the distance between consecutive stimuli in a stimulus sequence. When the distance from one stimulus to the next is constant, and the time elapsed from one stimulus to the next is also constant, subjects tend to judge the distances, correctly, as equal. However, if the distance from one stimulus to the next is constant, but the time elapsed from one stimulus to the next is not constant, then subjects tend to misperceive the interval that has the shorter temporal interval as also having a shorter spatial interval. Thus, the tau effect reveals that stimulus timing affects the perception of stimulus spacing. Time is also a perceived quantity and subject to its own illusions; research indicates that in the tau effect, perceived stimulus spacing follows perceived (phenomenal) time rather than actual (physical) time.
A sensory cue is a statistic or signal that can be extracted from the sensory input by a perceiver, that indicates the state of some property of the world that the perceiver is interested in perceiving.
The flash lag illusion or flash-lag effect is a visual illusion wherein a flash and a moving object that appear in the same location are perceived to be displaced from one another. Several explanations for this simple illusion have been explored in the neuroscience literature.
The cutaneous rabbit illusion is a tactile illusion evoked by tapping two or more separate regions of the skin in rapid succession. The illusion is most readily evoked on regions of the body surface that have relatively poor spatial acuity, such as the forearm. A rapid sequence of taps delivered first near the wrist and then near the elbow creates the sensation of sequential taps hopping up the arm from the wrist towards the elbow, although no physical stimulus was applied between the two actual stimulus locations. Similarly, stimuli delivered first near the elbow then near the wrist evoke the illusory perception of taps hopping from elbow towards wrist. The illusion was discovered by Frank Geldard and Carl Sherrick of Princeton University, in the early 1970s, and further characterized by Geldard (1982) and in many subsequent studies. Geldard and Sherrick likened the perception to that of a rabbit hopping along the skin, giving the phenomenon its name. While the rabbit illusion has been most extensively studied in the tactile domain, analogous sensory saltation illusions have been observed in audition and vision. The word "saltation" refers to the leaping or jumping nature of the percept.
Two-point discrimination (2PD) is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is. In clinical settings, two-point discrimination is a widely used technique for assessing tactile perception. It relies on the ability and/or willingness of the patient to subjectively report what they are feeling and should be completed with the patient’s eyes closed. The therapist may use calipers or simply a reshaped paperclip to do the testing. The therapist may alternate randomly between touching the patient with one point or with two points on the area being tested. The patient is asked to report whether one or two points was felt. The smallest distance between two points that still results in the perception of two distinct stimuli is recorded as the patient's two-point threshold. Performance on the two extremities can be compared for discrepancies. Although the test is still commonly used clinically, it has been roundly criticized by many researchers as providing an invalid measure of tactile spatial acuity, and several highly regarded alternative tests have been proposed to replace it.
Haptic perception means literally the ability "to grasp something". Perception in this case is achieved through the active exploration of surfaces and objects by a moving subject, as opposed to passive contact by a static subject during tactile perception.
The somatosensory system is a part of the sensory nervous system. The somatosensory system is a complex system of sensory neurons and neural pathways that responds to changes at the surface or inside the body. The axons of sensory neurons connect with, or respond to, various receptor cells. These sensory receptor cells are activated by different stimuli such as heat and nociception, giving a functional name to the responding sensory neuron, such as a thermoreceptor which carries information about temperature changes. Other types include mechanoreceptors, chemoreceptors, and nociceptors which send signals along a sensory nerve to the spinal cord where they may be processed by other sensory neurons and then relayed to the brain for further processing. Sensory receptors are found all over the body including the skin, epithelial tissues, muscles, bones and joints, internal organs, and the cardiovascular system.
Perceptual learning is learning better perception skills such as differentiating two musical tones from one another or categorizations of spatial and temporal patterns relevant to real-world expertise. Examples of this may include reading, seeing relations among chess pieces, and knowing whether or not an X-ray image shows a tumor.
In psychology, visual capture is the dominance of vision over other sense modalities in creating a percept. In this process, the visual senses influence the other parts of the somatosensory system, to result in a perceived environment that is not congruent with the actual stimuli. Through this phenomenon, the visual system is able to disregard what other information a different sensory system is conveying, and provide a logical explanation for whatever output the environment provides. Visual capture allows one to interpret the location of sound as well as the sensation of touch without actually relying on those stimuli but rather creating an output that allows the individual to perceive a coherent environment.
Haptic memory is the form of sensory memory specific to touch stimuli. Haptic memory is used regularly when assessing the necessary forces for gripping and interacting with familiar objects. It may also influence one's interactions with novel objects of an apparently similar size and density. Similar to visual iconic memory, traces of haptically acquired information are short lived and prone to decay after approximately two seconds. Haptic memory is best for stimuli applied to areas of the skin that are more sensitive to touch. Haptics involves at least two subsystems; cutaneous, or everything skin related, and kinesthetic, or joint angle and the relative location of body. Haptics generally involves active, manual examination and is quite capable of processing physical traits of objects and surfaces.
Visuo-haptic mixed reality (VHMR) is a branch of mixed reality that has the ability of merging visual and tactile perceptions of both virtual and real objects with a collocated approach. The first known system to overlay augmented haptic perceptions on direct views of the real world is the Virtual Fixtures system developed in 1992 at the US Air Force Research Laboratories. Like any emerging technology, the development of the VHMR systems is accompanied by challenges that, in this case, deal with the efforts to enhance the multi-modal human perception with the user-computer interface and interaction devices at the moment available. Visuo-haptic mixed reality (VHMR) consists of adding to a real scene the ability to see and touch virtual objects. It requires the use of see-through display technology for visually mixing real and virtual objects and haptic devices necessary to provide haptic stimuli to the user while interacting with the virtual objects. A VHMR setup allows the user to perceive visual and kinesthetic stimuli in a co-located manner, i.e., the user can see and touch virtual objects at the same spatial location. This setup overcomes the limits of the traditional one, i.e, display and haptic device, because the visuo-haptic co-location of the user's hand and a virtual tool improve the sensory integration of multimodal cues and makes the interaction more natural. But it also comes with technological challenges in order to improve the naturalness of the perceptual experience.
Vincent Hayward, born January 5, 1955 in Paris, is an engineer specializing in touch and haptics. He is a professor at Sorbonne University, Institute of Intelligent Systems and Robotics (ISIR), where since 2008 he leads a team dedicated to the study of haptic perception and the creation of tactile stimulation devices. In 2020, he was elected to the French Academy of sciences.
