skin surface (e.g., edges, curvature, and texture) and proprioception of hand position and conformation. people can rapidly and accurately identify three-dimensional objects by touch. this involves exploratory procedures, such as moving the fingers over the outer surface of the object or holding the entire object in the hand. haptic perception relies on the forces experienced during touch. gibson defined the haptic system as "the sensibility of the individual to the world adjacent to his body by use of his body." gibson and others emphasized the close link between body movement and haptic perception, where the latter is active exploration. the concept of haptic perception is related to the concept of extended physiological proprioception according to which, when using a tool such as a stick, perceptual experience is transparently transferred to the end of the tool. taste main article: tastetaste (formally known as gustation) is the ability to perceive the flavor of substances, including, but not limited to, food. humans receive tastes through sensory organs concentrated on the upper surface of the tongue, called taste buds or gustatory calyculi. the human tongue has 100 to 150 taste receptor cells on each of its roughly-ten thousand taste buds. traditionally, there have been four primary tastes: sweetness, bitterness, sourness, and saltiness. the recognition and awareness of umami, which is considered the fifth primary taste, is a relatively recent development in western cuisine. other tastes can be mimicked by combining these basic tastes, all of which contribute only partially to the sensation and flavor of food in the mouth. other factors include smell, which is detected by the olfactory epithelium of the nose; texture, which is detected through a variety of mechanoreceptors, muscle nerves, etc.; and temperature, which is detected by thermoreceptors. all basic tastes are classified as either appetitive or aversive, depending upon whether the things they sense are harmful or beneficial. smell main article: olfaction smell is the process of absorbing molecules through olfactory organs, which are absorbed by humans through the nose. these molecules diffuse through a thick layer of mucus; come into contact with one of thousands of cilia that are projected from sensory neurons; and are then absorbed into a receptor (one of 347 or so). it is this process that causes humans to understand the concept of smell from a physical standpoint. smell is also a very interactive sense as scientists have begun to observe that olfaction comes into contact with the other sense in unexpected ways. it is also the most primal of the senses, as it is known to be the first indicator of safety or danger, therefore being the sense that drives the most basic of human survival skills. as such, it can be a catalyst for human behavior on a subconscious and instinctive level. social social perception is the part of perception that allows people to understand the individuals and groups of their social world. thus, it is an element of social cognition.though the phrase "i owe you" can be heard as three distinct words, a spectrogram reveals no clear boundaries. speech speech perception is the process by which spoken language is heard, interpreted and understood. research in this field seeks to understand how human listeners recognize the sound of speech (or phonetics) and use such information to understand spoken language. listeners manage to perceive words across a wide range of conditions, as the sound of a word can vary widely according to words that surround it and the tempo of the speech, as well as the physical characteristics, accent, tone, and mood of the speaker. reverberation, signifying the persistence of sound after the sound is produced, can also have a considerable impact on perception. experiments have shown that people automatically compensate for this effect when hearing speech. the process of perceiving speech begins at the level of the sound within the auditory signal and the process of audition. the initial auditory signal is compared with visual information—primarily lip movement—to extract acoustic cues and phonetic information. it is possible other sensory modalities are integrated at this stage as well. this speech information can then be used for higher-level language processes, such as word recognition. speech perception is not necessarily uni-directional. higher-level language processes connected with morphology, syntax, and/or semantics may also interact with basic speech perception processes to aid in recognition of speech sounds. it may be the case that it is not necessary (maybe not even possible) for a listener to recognize phonemes before recognizing higher units, such as words. in an experiment, richard m. warren replaced one phoneme of a word with a cough-like sound. his subjects restored the missing speech sound perceptually without any difficulty. moreover, they were not able to accurately identify which phoneme had even been disturbed. faces facial perception refers to cognitive processes specialized in handling human faces (including perceiving the identity of an individual) and facial expressions (such as emotional cues.) social touch main article: somatosensory system § neural processing of social touchthe somatosensory cortex is a part of the brain that receives and encodes sensory information from receptors of the entire body. affective touch is a type of sensory information that elicits an emotional reaction and is usually social in nature. such information is actually coded differently than other sensory information. though the intensity of affective touch is still encoded in the primary somatosensory cortex, the feeling of pleasantness associated with affective touch is activated more in the anterior cingulate cortex. increased blood oxygen level-dependent (bold) contrast imaging, identified during functional magnetic resonance imaging (fmri), shows that signals in the anterior cingulate cortex, as well as the prefrontal cortex, are highly correlated with pleasantness scores of affective touch. inhibitory transcranial magnetic stimulation (tms) of the primary somatosensory cortex inhibits the perception of affective touch intensity, but not affective touch pleasantness. therefore, the s1 is not directly involved in processing socially affective touch pleasantness, but still plays a role in discriminating touch location and intensity. multi-modal perception multi-modal perception refers to concurrent stimulation in more than one sensory modality and the effect such has on the perception of events and objects in the world. time (chronoception) chronoception refers to how the passage of time is perceived and experienced. although the sense of time is not associated with a specific sensory system, the work of psychologists and neuroscientists indicates that human brains do have a system governing the perception of time, composed of a highly distributed system involving the cerebral cortex, cerebellum, and basal ganglia. one particular component of the brain, the suprachiasmatic nucleus, is responsible for the circadian rhythm (commonly known as one's "internal clock"), while other cell clusters appear to be capable of shorter-range timekeeping, known as an ultradian rhythm. one or more dopaminergic pathways in the central nervous system appear to have a strong modulatory influence on mental chronometry, particularly interval timing. agency sense of agency refers to the subjective feeling of having chosen a particular action. some conditions, such as schizophrenia, can cause a loss of this sense, which may lead a person into delusions, such as feeling like a machine or like an outside source is controlling them. an opposite extreme can also occur, where people experience everything in their environment as though they had decided that it would happen. even in non-pathological cases, there is a measurable difference between the making of a decision and the feeling of agency. through methods such as the libet experiment, a gap of half a second or more can be detected from the time when there are detectable neurological signs of a decision having been made to the time when the subject actually becomes conscious of the decision. there are also experiments in which an illusion of agency is induced in psychologically normal subjects. in 1999, psychologists wegner and wheatley gave subjects instructions to move a mouse around a scene and point to an image about once every thirty seconds. however, a second person—acting as a test subject but actually a confederate—had their hand on the mouse at the same time, and controlled some of the movement. experimenters were able to arrange for subjects to perceive certain "forced stops" as if they were their own choice. familiarity recognition memory is sometimes divided into two functions by neuroscientists: familiarity and recollection. a strong sense of familiarity can occur without any recollection, for example in cases of deja vu. the temporal lobe (specifically the perirhinal cortex) responds differently to stimuli that feel novel compared to stimuli that feel familiar. firing rates in the perirhinal cortex are connected with the sense of familiarity in humans and other mammals. in tests, stimulating this area at 10–15 hz caused animals to treat even novel images as familiar, and stimulation at 30–40 hz caused novel images to be partially treated as familiar. in particular, stimulation at 30–40 hz led to animals looking at a familiar image for longer periods, as they would for an unfamiliar one, though it did not lead to the same exploration behavior normally associated with novelty. recent studies on lesions in the area concluded that rats with a damaged perirhinal cortex were still more interested in exploring when novel objects were present, but seemed unable to tell novel objects from familiar ones—they examined both equally. thus, other brain regions are involved with noticing unfamiliarity, while the perirhinal cortex is needed to associate the feeling with a specific source. sexual stimulation sexual stimulation is any stimulus (including bodily contact) that leads to, enhances, and maintains sexual arousal, possibly even leading to orgasm. distinct from the general sense of touch, sexual stimulation is strongly tied to hormonal activity and chemical triggers in the body. although sexual arousal may arise without physical stimulation, achieving orgasm usually requires physical sexual stimulation (stimulation of the krause-finger corpuscles found in erogenous zones of the body.) other senses main article: senseother senses enable perception of body balance, acceleration, gravity, position of body parts, temperature, and pain. they can also enable perception of internal senses, such as suffocation, gag reflex, abdominal distension, fullness of rectum and urinary bladder, and sensations felt in the throat and lungs. reality in the case of visual perception, some people can see the percept shift in their mind's eye. others, who are not picture thinkers, may not necessarily perceive the 'shape-shifting' as their world changes. this esemplastic nature has been demonstrated by an experiment that showed that ambiguous images have multiple interpretations on the perceptual level. the confusing ambiguity of perception is exploited in human technologies such as camouflage and biological mimicry. for example, the wings of european peacock butterflies bear eyespots that birds respond to as though they were the eyes of a dangerous predator. there is also evidence that the brain in some ways operates on a slight "delay" in order to allow nerve impulses from distant parts of the body to be integrated into simultaneous signals. perception is one of the oldest fields in psychology. the oldest quantitative laws in psychology are weber's law, which states that the smallest noticeable difference in stimulus intensity is proportional to the intensity of the reference; and fechner's law, which quantifies the relationship between the intensity of the physical stimulus and its perceptual counterpart (e.g., testing how much darker a computer screen can get before the viewer actually notices). the study of perception gave rise to the gestalt school of psychology, with an emphasis on holistic approach. physiology main article: sensory systema sensory system is a part of the nervous system responsible for processing sensory information. a sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. commonly recognized sensory systems are those for vision, hearing, somatic sensation (touch), taste and olfaction (smell), as listed above. it has been suggested that the immune system is an overlooked sensory modality. in short, senses are transducers from the physical world to the realm of the mind. the receptive field is the specific part of the world to which a receptor organ and receptor cells respond. for instance, the part of the world an eye can see, is its receptive field; the light that each rod or cone can see, is its receptive field. receptive fields have been identified for the visual system, auditory system and somatosensory system, so far. research attention is currently focused not