During every moment of an organism's life, sensory information is being taken in by sensory receptors and processed by the nervous system. Sensory information is stored in sensory memory just long enough to be transferred to short-term memory. Humans have five main senses: sight, hearing, taste, smell, touch. Sensory memory (SM) allows individuals to retain impressions of sensory information after the original stimulus has ceased. A common demonstration of SM is a child's ability to write letters and make circles by twirling a sparkler at night. When the sparkler is spun fast enough, it appears to leave a trail which forms a continuous image. This "light trail" is the image that is represented in the visual sensory store known as iconic memory. The other two types of SM that have been most extensively studied are echoic memory, and haptic memory; however, it is reasonable to assume that each physiological sense has a corresponding memory store. Children for example have been shown to remember specific "sweet" tastes during incidental learning trials but the nature of this gustatory store is still unclear.
SM is considered to be outside of cognitive control and is instead an automatic response. The information represented in SM is the "raw data" which provides a snapshot of a person's overall sensory experience. Common features between each sensory modality have been identified; however, as experimental techniques advance, exceptions and additions to these general characteristics will surely evolve. The auditory store, echoic memory, for example, has been shown to have a temporal characteristic in which the timing and tempo of a presented stimulus affects transfer into more stable forms of memory. Four common features have been identified for all forms of SM:
- The formation of a SM trace is independent of attention to the stimulus.
- The information stored in SM is modality specific. This means for example, that echoic memory is for the exclusive storage of auditory information, and haptic memory is for the exclusive storage of tactile information.
- Each SM store represents an immense amount of detail resulting in very high resolution of information.
- Each SM store is very brief and lasts a very short period of time. Once the SM trace has decayed or is replaced by a new memory, the information stored is no longer accessible and is ultimately lost. All SM stores have slightly different durations which is discussed in more detail on their respective pages.
It is widely accepted that all forms of SM are very brief in duration; however, the approximated duration of each memory store is not static. Iconic memory for example has an average duration of 500 ms which tends to decrease with age. The SM is made up of spatial or categorical stores of different kinds of information, each subject to different rates of information processing and decay. Genetics also play a role in SM capacity; mutations to the brain-derived neurotrophic factor (BDNF), a nerve growth factor, and N-methyl-D-aspartate (NMDA) receptors, responsible for synaptic plasticity, decrease iconic and echoic memory capacities respectively.
Iconic memory. The mental representation of the visual stimuli are referred to as icons (fleeting images.) Iconic memory was the first sensory store to be investigated with experiments dating back as far as 1740. One of the earliest investigations into this phenomenon was by Ján Andrej Segner, a German physicist and mathematician. In his experiment, Segner attached a glowing coal to a cart wheel and rotated the wheel at increasing speed until an unbroken circle of light was perceived by the observer. He calculated that the glowing coal needed to make a complete circle in under 100ms to achieve this effect, which he determined was the duration of this visual memory store.
Echoic memory represents SM for the auditory sense of hearing. Auditory information travels as sound waves which are sensed by hair cells in the ears. Information is sent to and processed in the temporal lobe. The first studies of echoic memory came shortly after Sperling investigated iconic memory using an adapted partial report paradigm. Today, characteristics of echoic memory have been found mainly using a Mismatch Negativity (MMN) paradigm which utilizes EEG and MEG recordings. MMN has been used to identify some of the key roles of echoic memory such as change detection and language acquisition. Change detection, or the ability to detect an unusual or possibly dangerous change in the environment independent of attention, is key to the survival of an organism. With regards to language, a characteristic of children who begin speaking late in development is reduced duration of echoic memory. In short," Echoic Memory is a fast - decaying store of auditory information  In the case of damage to or lesions developing on the frontal lobe, parietal lobe, or hippocampus, echoic memory will likely be shortened and/or have a slower reaction time.
Haptic memory represents SM for the tactile sense of touch. Sensory receptors all over the body detect sensations such as pressure, itching, and pain. Information from receptors travel through afferent neurons in the spinal cord to the postcentral gyrus of the parietal lobe in the brain. This pathway comprises the somatosensory system. Evidence for haptic memory has only recently been identified resulting in a small body of research regarding its role, capacity, and duration. Already however, fMRI studies have revealed that specific neurons in the prefrontal cortex are involved in both SM, and motor preparation which provides a crucial link to haptic memory and its role in motor responses.
Relationship with other memory systems
SM is not involved in higher cognitive functions such as consolidation of memory traces or comparison of information. Likewise, the capacity and duration of SM cannot be influenced by top-down control; a person cannot consciously think or choose what information is stored in SM, or how long it will be stored for. The role of SM is to provide a detailed representation of our entire sensory experience for which relevant pieces of information can be extracted by short-term memory (STM) and processed by working memory (WM). STM is capable of storing information for 10–15 seconds without rehearsal while working memory actively processes, manipulates, and controls the information. Information from STM can then be consolidated into long-term memory where memories can last a lifetime. The transfer of SM to STM is the first step in the Atkinson–Shiffrin memory model which proposes a structure of memory.
- Carlson, Neil R. (2010). Psychology the science of behavior. Pearson Canada Inc. p. 232. ISBN 9780205645244.
- Coltheart, Max (1980). "Iconic memory and visible persistence". Perception & Psychophysics 27 (3): 183–228. doi:10.3758/BF03204258.
- Laureati, M.; E. Pagliarini; J. Mojet; E. Köster (April 2011). "Incidental learning and memory for food varied in sweet taste in children". Food Quality and Preference 22 (3): 264–270. doi:10.1016/j.foodqual.2010.11.002.
- Winkler, Istvan; Nelson Cowan (2005). "From Sensory to Long-Term Memory Evidence from Auditory Memory Reactivation Studies". Experimental Psychology 52 (1): 3–20. doi:10.1027/1618-3126.96.36.199.
- Walsh, David; Larry Thompson (1978). "Age Differences in Visual Sensory Memory". Journal of Gerontology 33 (3): 383–387. doi:10.1093/geronj/33.3.383. PMID 748430.
- Irvine, Elizabeth (2011). "Rich Experience and Sensory Memory". Philosophical Psychology 24 (2): 159–176. doi:10.1080/09515089.2010.543415.
- Javitt, Daniel; Mitchell Steinscheider; Charles Schroeder; Joseph Arezzo (October 1996). "Role of cortical N-methyl-D-aspartate receptors in auditory sensory memory and mismatch negativity generation: implications for schizophrenia". Proceedings of the National Academy of Sciences USA 93: 11962–11967. doi:10.1073/pnas.93.21.11962.
- Beste, Christian; Daniel Schneider; Jörg Epplen; Larissa Arning (2011-02/2011-03). "The functional BDNF Val66Met polymorphism affects functions of pre-attentive visual sensory memory processes". Neuropharmacology 60 (2-3): 467–471. doi:10.1016/j.neuropharm.2010.10.028. PMID 21056046. Check date values in:
- Darwin; Turvey, Crowder (1972). "An auditory analogue of the sperling partial report procedure: Evidence for brief auditory storage" (PDF). Cognitive Psychology 3: 255–267. doi:10.1016/0010-0285(72)90007-2. Retrieved 2011-03-09.
- Sabri; Kareken, Dzemidzic; Lowe, Melara (2003). "Neural correlates of auditory sensory memory and automatic change detection". NeuroImage 21 (1): 69–74. doi:10.1016/j.neuroimage.2003.08.033. PMID 14741643.
- Grossheinrich, Nicola; Stefanie Kademann; Jennifer Bruder; Juergen Bartling; Waldemar Von Suchodoletz (January 2010). "Auditory sensory memory and language abilities in former late talkers: A mismatch negativity study". Psychophysiology 47 (5): 822–830. doi:10.1111/j.1469-8986.2010.00996.x.
- Schacter, Daniel L (2009–2011). PYCHOLOGY. Catherine Woods. p. 226. ISBN 978- 1 - 4- 292- 3719- 2.
- Claude, Alain; David L. Woods; Robert T. Knight (23 November 1998). "A distributed cortical network for auditory sensory memory in humans". Brain Research 812 (1-2): 23–37. doi:10.1016/S0006-8993(98)00851-8. PMID 9813226. Retrieved 7 December 2012.
- Dubrowski, Carnahan, Shih (2009), "Evidence for Haptic Memory", Third Joint EuroHaptics conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, retrieved 2011-03-08
- D'Esposito, M.; D. Ballard; E. Zarahn; G. K. Aguirre (2002-03-15). "The Role of Prefrontal Cortex in Sensory Memory and Motor Preparation: An Event-Related fMRI Study". NeuroImage 11 (5): 400–408. doi:10.1006/nimg.2000.0571. PMID 10806027.
- Dick, A. O. (1974). "Iconic memory and its relation to perceptual processing and other memory mechanisms". Perception & Psychophysics 16 (3): 575–596. doi:10.3758/BF03198590.