Repetition priming refers to improvements in a behavioural response when stimuli are repeatedly presented. The improvements can be measured in terms of accuracy or reaction time and can occur when the repeated stimuli are either identical or similar to previous stimuli. [1] These improvements have been shown to be cumulative, so as the number of repetitions increases the responses get continually faster up to a maximum of around seven repetitions. [2] These improvements are also found when the repeated items are changed slightly in terms of orientation, [3] size [4] and position. [5] The size of the effect is also modulated by the length of time the item is presented for [6] and the length time between the first and subsequent presentations of the repeated items. [7]
Repetition priming can occur without a person being aware of either the repeats or the improvements in his/her response, so it is generally thought to involve implicit memory processes that are dissociable from explicit memory processes. [8] This idea has support from findings that amnesic patients with damage to limbic and/or diencephalic structures show measurable repetition priming effects but have deficits on explicit measures of memory. [9] [10] However, some researchers suggest that implicit and explicit memory systems are not in fact separate. [11] Repetition priming has also been associated with attentional processes, [12] stimulus expectation [13] and episodic memory. [14]
Research into repetition priming has been used to investigate the nature of mechanisms underlying the behavioural effects of rapid learning. In utilizing measures of repetition suppression, the putative neural correlate of repetition priming, and measuring changes in the neural response associated with changing the presented stimuli, researchers are attempting to index regions and their processing biases along perceptual, conceptual and response dimensions. [15] This area of research is based on multiple measurement methods from single cell recordings [16] to multi-regional measurements using functional magnetic resonance imaging (fMRI), [17] electroencephalography (EEG) [18] and magnetoencephalography (MEG). [19] Transcranial magnetic stimulation (TMS) has also been used to temporarily 'lesion' (inactivate) specific regions and so get an indication of the necessity of those regions in processing specific dimensions of the presented stimuli. [20] Much of this research has been focused on the visual domain, however auditory [21] and olfactory [22] processes have also been investigated.
Numerous models have been put forward to explain behavioural efficiencies that are gained with repeated presentations of the same or similar stimuli. These are outlined below.
In this model the attenuation of a neural response is hypothesised to be due to an overall reduction in the amplitude of a neuron's firing. [23] Whether this reduction occurs across all neurons that responded to the initial stimulus or just the critical subset of those that initially responded maximally, is still unclear. [24] However, evidence does suggest that a mechanism like this reduces redundant neural firing and enhances efficiencies in processing in the early visual cortex. [25]
Along similar lines is the idea that repetition causes the neurons that are less relevant to the representation of the stimulus to stop firing when that stimulus is repeated. [26] In this way the representation is supported by a gradually sparser response, resulting in an adaptive reduction in metabolic requirements and increased efficiencies in information transmission through the neural hierarchy. [24] This could be the result of lateral inhibition within representational levels in a competitive Hebbian learning system, where strong connections get stronger and inhibit the weaker connections. [24] Much of the evidence for this comes from primate studies of the inferotemporal cortex [27] and single cell recordings with long training periods. [28] However, decreases in firing rate over short-term training on repeated stimuli appear to be greatest in those cells that initially respond with the highest activation rate, [29] in line with the fatigue model above.
The key concept in this model is that information travels faster through the network when the current stimulus representation overlaps with a previous representation, driven by more rapid onset of neural activation with repeated presentations. [30] fMRI studies have been used in an attempt to measure these potential latency differences but the temporal resolution is not very precise [21] and single cell recordings typically do not show shortened latencies to repeated stimuli. [31] Another possible explanation of facilitation is synaptic potentiation within an attractor neural network model where repetition decreases the settling time as the attractor basin deepens and so increases the overall speed of processing. [32]
When a stimulus is repeated top-down feedback modulates the neural response of earlier processing regions, [33] with reduced neural activation and improved behavioural responses reflecting fulfilled expectations. [13] The idea for this comes from predictive coding theories and Bayesian statistics [34] and has some support in fMRI studies manipulating stimulus expectation. [13] However, the results may also reflect the involvement of attention, which seems to have a modulatory effect on the extent of priming elicited. [12]
This theory is based on the idea that because downstream neurons are sensitive to both the firing rates and the timing of those inputs, efficiencies in processing may be gained through synchronised activation. [35] Evidence of synchronisation associated with repeated stimuli include phase locking found between two regions of the cat visual cortex while measuring spike synchronisation for trained compared with novel stimuli [36] and suppressed firing and increased synchrony of spikes with repetition of odour puffs to locust's antennae. [37] Evidence using EEG and MEG suggests that stimulus repetition in humans results in increased synchrony between distinct cortical regions, often the same regions that show reduced local neural activity (see repetition suppression below). [38] [39] In one study, the timing of this across-region synchronization predicted the amount of behavioral facilitation seen with repetition priming, suggestive of a close link between synchrony and behavior. [38]
This theory suggests that repetition priming is a result of binding the initial stimulus directly to the response while bypassing the intervening layers of computation. [40] The mechanism mediating this direct binding has not been clarified but several hypotheses have been put forward. One theory explains it as a race between automatic activation of a previous stimulus-response route and the reengagement of the "algorithmic" route [41] and another theory suggests the operation of an "action-trigger" where repeated stimuli trigger the previous response through perceptual or conceptual associations with the original stimulus. [42] In support of this theory is evidence of a response congruency effect, which would be expected from these stimulus-response bindings. [43] The increased synchrony between regions discussed above could be a neural correlate of stimulus-response binding. [38]
The phenomenon of repetition suppression, a reduction in neural activity when stimuli are repeated, is thought to depend on processing overlaps between repeated items [44] and is generally considered to be the neural correlate of repetition priming. As such it has been used extensively in research investigating the nature of representations across various levels of the visual processing hierarchy. [15] In doing so researchers have found that repetition suppression appears to occur on multiple processing levels; dependent on the stimuli being processed and the processing level at which the experimental manipulation is directed; with reductions in neural activity to repeated stimuli occurring in regions involved with the initial processing of those features. [45] However, care must be taken in interpreting the results of these studies as the relationship between repetition suppression and repetition priming has not been definitively established. [46]
Although repetition priming is most often associated with neural attenuation for repeated presentation of stimuli, increases in neural responses have also been measured in a number of experimental contexts. For example, when performing mathematical calculations, [47] when repeated stimuli are degraded, [48] in studies involving a backward masking paradigm [30] and when stimuli have no pre-existing associations or meaning. [49]
The consciousness and binding problem is the problem of how objects, background and abstract or emotional features are combined into a single experience.
A gamma wave or gamma rhythm is a pattern of neural oscillation in humans with a frequency between 25 and 140 Hz, the 40 Hz point being of particular interest. Gamma rhythms are correlated with large-scale brain network activity and cognitive phenomena such as working memory, attention, and perceptual grouping, and can be increased in amplitude via meditation or neurostimulation. Altered gamma activity has been observed in many mood and cognitive disorders such as Alzheimer's disease, epilepsy, and schizophrenia. Elevated gamma activity has also been observed in moments preceding death.
The N400 is a component of time-locked EEG signals known as event-related potentials (ERP). It is a negative-going deflection that peaks around 400 milliseconds post-stimulus onset, although it can extend from 250-500 ms, and is typically maximal over centro-parietal electrode sites. The N400 is part of the normal brain response to words and other meaningful stimuli, including visual and auditory words, sign language signs, pictures, faces, environmental sounds, and smells.
Neural binding is the neuroscientific aspect of what is commonly known as the binding problem: the interdisciplinary difficulty of creating a comprehensive and verifiable model for the unity of consciousness. "Binding" refers to the integration of highly diverse neural information in the forming of one's cohesive experience. The neural binding hypothesis states that neural signals are paired through synchronized oscillations of neuronal activity that combine and recombine to allow for a wide variety of responses to context-dependent stimuli. These dynamic neural networks are thought to account for the flexibility and nuanced response of the brain to various situations. The coupling of these networks is transient, on the order of milliseconds, and allows for rapid activity.
Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response. Sensitization often is characterized by an enhancement of response to a whole class of stimuli in addition to the one that is repeated. For example, repetition of a painful stimulus may make one more responsive to a loud noise.
In cognitive science and neuropsychology, executive functions are a set of cognitive processes that are necessary for the cognitive control of behavior: selecting and successfully monitoring behaviors that facilitate the attainment of chosen goals. Executive functions include basic cognitive processes such as attentional control, cognitive inhibition, inhibitory control, working memory, and cognitive flexibility. Higher-order executive functions require the simultaneous use of multiple basic executive functions and include planning and fluid intelligence.
Sensory neuroscience is a subfield of neuroscience which explores the anatomy and physiology of neurons that are part of sensory systems such as vision, hearing, and olfaction. Neurons in sensory regions of the brain respond to stimuli by firing one or more nerve impulses following stimulus presentation. How is information about the outside world encoded by the rate, timing, and pattern of action potentials? This so-called neural code is currently poorly understood and sensory neuroscience plays an important role in the attempt to decipher it. Looking at early sensory processing is advantageous since brain regions that are "higher up" contain neurons which encode more abstract representations. However, the hope is that there are unifying principles which govern how the brain encodes and processes information. Studying sensory systems is an important stepping stone in our understanding of brain function in general.
Neural coding is a neuroscience field concerned with characterising the hypothetical relationship between the stimulus and the individual or ensemble neuronal responses and the relationship among the electrical activity of the neurons in the ensemble. Based on the theory that sensory and other information is represented in the brain by networks of neurons, it is thought that neurons can encode both digital and analog information.
The mismatch negativity (MMN) or mismatch field (MMF) is a component of the event-related potential (ERP) to an odd stimulus in a sequence of stimuli. It arises from electrical activity in the brain and is studied within the field of cognitive neuroscience and psychology. It can occur in any sensory system, but has most frequently been studied for hearing and for vision, in which case it is abbreviated to vMMN. The (v)MMN occurs after an infrequent change in a repetitive sequence of stimuli For example, a rare deviant (d) stimulus can be interspersed among a series of frequent standard (s) stimuli. In hearing, a deviant sound can differ from the standards in one or more perceptual features such as pitch, duration, loudness, or location. The MMN can be elicited regardless of whether someone is paying attention to the sequence. During auditory sequences, a person can be reading or watching a silent subtitled movie, yet still show a clear MMN. In the case of visual stimuli, the MMN occurs after an infrequent change in a repetitive sequence of images.
Negative priming is an implicit memory effect in which prior exposure to a stimulus unfavorably influences the response to the same stimulus. It falls under the category of priming, which refers to the change in the response towards a stimulus due to a subconscious memory effect. Negative priming describes the slow and error-prone reaction to a stimulus that is previously ignored. For example, a subject may be imagined trying to pick a red pen from a pen holder. The red pen becomes the target of attention, so the subject responds by moving their hand towards it. At this time, they mentally block out all other pens as distractors to aid in closing in on just the red pen. After repeatedly picking the red pen over the others, switching to the blue pen results in a momentary delay picking the pen out. The slow reaction due to the change of the distractor stimulus to target stimulus is called the negative priming effect.
In cognitive neuroscience, visual modularity is an organizational concept concerning how vision works. The way in which the primate visual system operates is currently under intense scientific scrutiny. One dominant thesis is that different properties of the visual world require different computational solutions which are implemented in anatomically/functionally distinct regions that operate independently – that is, in a modular fashion.
Priming is the idea that exposure to one stimulus may influence a response to a subsequent stimulus, without conscious guidance or intention. The priming effect refers to the positive or negative effect of a rapidly presented stimulus on the processing of a second stimulus that appears shortly after. Generally speaking, the generation of priming effect depends on the existence of some positive or negative relationship between priming and target stimuli. For example, the word nurse might be recognized more quickly following the word doctor than following the word bread. Priming can be perceptual, associative, repetitive, positive, negative, affective, semantic, or conceptual. Priming effects involve word recognition, semantic processing, attention, unconscious processing, and many other issues, and are related to differences in various writing systems. Research, however, has yet to firmly establish the duration of priming effects, yet their onset can be almost instantaneous.
The oddball paradigm is an experimental design used within psychology research. Presentations of sequences of repetitive stimuli are infrequently interrupted by a deviant stimulus. The reaction of the participant to this "oddball" stimulus is recorded.
Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task-demand to the brain can appear to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade. This elicits an overestimation in the temporal duration for which that target stimulus was perceived. This effect can extend apparent durations by up to half a second and is consistent with the idea that the visual system models events prior to perception.
Many experiments have been done to find out how the brain interprets stimuli and how animals develop fear responses. The emotion, fear, has been hard-wired into almost every individual, due to its vital role in the survival of the individual. Researchers have found that fear is established unconsciously and that the amygdala is involved with fear conditioning.
Visual masking is a phenomenon of visual perception. It occurs when the visibility of one image, called a target, is reduced by the presence of another image, called a mask. The target might be invisible or appear to have reduced contrast or lightness. There are three different timing arrangements for masking: forward masking, backward masking, and simultaneous masking. In forward masking, the mask precedes the target. In backward masking the mask follows the target. In simultaneous masking, the mask and target are shown together. There are two different spatial arrangements for masking: pattern masking and metacontrast. Pattern masking occurs when the target and mask locations overlap. Metacontrast masking occurs when the mask does not overlap with the target location.
Surround suppression is where the relative firing rate of a neuron may under certain conditions decrease when a particular stimulus is enlarged. It has been observed in electrophysiology studies of the brain and has been noted in many sensory neurons, most notably in the early visual system. Surround suppression is defined as a reduction in the activity of a neuron in response to a stimulus outside its classical receptive field.
The bi-directional hypothesis of language and action proposes that the sensorimotor and language comprehension areas of the brain exert reciprocal influence over one another. This hypothesis argues that areas of the brain involved in movement and sensation, as well as movement itself, influence cognitive processes such as language comprehension. In addition, the reverse effect is argued, where it is proposed that language comprehension influences movement and sensation. Proponents of the bi-directional hypothesis of language and action conduct and interpret linguistic, cognitive, and movement studies within the framework of embodied cognition and embodied language processing. Embodied language developed from embodied cognition, and proposes that sensorimotor systems are not only involved in the comprehension of language, but that they are necessary for understanding the semantic meaning of words.
Social cognitive neuroscience is the scientific study of the biological processes underpinning social cognition. Specifically, it uses the tools of neuroscience to study "the mental mechanisms that create, frame, regulate, and respond to our experience of the social world". Social cognitive neuroscience uses the epistemological foundations of cognitive neuroscience, and is closely related to social neuroscience. Social cognitive neuroscience employs human neuroimaging, typically using functional magnetic resonance imaging (fMRI). Human brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct-current stimulation are also used. In nonhuman animals, direct electrophysiological recordings and electrical stimulation of single cells and neuronal populations are utilized for investigating lower-level social cognitive processes.
Laura Busse is a German neuroscientist and professor of Systemic Neuroscience within the Division of Neurobiology at the Ludwig Maximilian University of Munich. Busse's lab studies context-dependent visual processing in mouse models by performing large scale in vivo electrophysiological recordings in the thalamic and cortical circuits of awake and behaving mice.