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Visual Antipriming
Visual antipriming is a phenomenon [1] which involves an impairment in identification of visual stimuli due to their visual similarities with other visual stimuli which have been recently viewed. For example recently viewing a piano impairs the identification of similar objects which have common features, like a table as both objects contain legs. Because the piano has been recently encoded and primed, when the brain views the shared features (legs) it automatically wants to identify the object as the familiar object, therefore the individual will take longer to identify what the actual object is. Unlike in priming, where the viewer benefits from familiar stimuli, antipriming leads to a disadvantage. Therefore the effect may be defined as a significant reduction in the accuracy for identifying visual items that are similar, but different in some aspects from items recently processed.

Marsolek et al. (2006)[2] propose that visual antipriming is the result of many synaptic modifications, due to the exposure of different visual items which overlap in some way, and therefore are represented in an overlapping format in the posterior neocortex[3]. This overlap in the representations of items, for example the leg that belongs to a table and a piano, occurs due to the process of strengthening the connections between appropriate units, such as viewing a piano many times strengthens the ability to identify it. However the strengthening of some connections, such as the beneficial efficiency in identifying a piano, also lead to the weakening of other visual items which contain overlapping connections and are not required for the current item, for example the parts that make an item a table rather than a piano. In this way, the next time an antiprimed object is identified, the strengthening of its shape representation will help to maintain it in the system.

Visual Antipriming and Priming
Antipriming is directly related to priming, which is a repetition effect where identification of an item can be improved due to prior experience with the particular item (repetition priming), or a related item (conceptual or semantic priming). For example, recently viewing a piano typically facilitates an enhanced identification of pianos for some period after (repetition priming), as well as stimuli that conceptually relate to a piano, for example other instruments (conceptual or semantic priming). Because priming does not require awareness, it is considered an important example of implicit or non-conscious memory [4], therefore strengthening one representation after its usage causes priming for that item, but also antipriming for some other, non-repeated items. Antipriming is thus, the detriment of this beneficial effect and demonstrates the cost of priming.

Theory of Overlapping Representations
Visual antipriming begins with the question of whether the representations of different items are stored in seperate or overlapping manners in the brain[5]. Past cognitive models and theories support localist/discrete representations within the brain, where different items are stored with their own traces[6][7][8][9][10][11][12]. However other cognitive models suggest that aspects of items which belong to multiple objects have superimposed representations, therefore different items are stored in distributed and overlapping ways [13][14][15][16][17][18][19]

Visual antipriming provides functional evidence for the cognitive models which suggest superimposed representations of visual objects, with there being a continual adjustment of repetition priming effects[20]. Support for the theory of overlapping representations comes from neuroimaging studies [21][22] where overlapping representations have been indicated by patterns of activation from different classes of shapes that overlap in the human ventral cortex. This overlap between representations is beneficial as it increases the efficiency of storage [23] and generalisation abilities, however has negative impacts in terms of learning new objects [24][25]. Marsolek et al. (2006)[26] theorised that partially superimposed representations in the neocortex represent familiar visual object shapes, and that these traces undergo continual adjustments, and that representations of objects are strengthened after every time they are identified due to small representational changes. This strengthening is responsible for repetition priming for that object but also leads to antipriming of other objects which have superimposed representations with the primed object [27]. Therefore, some of the changes that enhance the ability to reactivate the representation for the primed object (piano) simultaneously weaken the connections of other overlapping objects, and result in an impairment in the ability to activate the specific representations of these other objects [28].

Marsolek et al.'s Experiment:
Marsolek et al.'s original experiment[29] comprised of three main phases. These included participants viewing and identifying a set of briefly presented objects, which provided a baseline measure of visual object identification performance, against which both priming and antipriming would be measured. Followed by participants viewing and judging a new set of visual objects, presumably, the visual representations of these objects would be strengthened during this phase. Finally participants again viewed and identified briefly presented objects, however in this final phase, half of the objects were viewed in the immediately preceding phase (primed), and the other half were different from all previously presented objects (antiprimed).

Perceptual identification of very briefly presented objects is used in the baseline, primed, and antiprimed conditions to increase the degree to which visual processing underlies performance in those conditions. Priming was measured as more accurate performance in the primed condition than in the baseline condition, and antipriming was measured as less accurate performance in the antiprimed condition than in the baseline condition. The results demonstrated that antiprimed objects were identified less accurately than objects presented in the baseline condition, and primed objects were identified more accurately than baseline objects. The magnitude of the antiprimed effect was also significantly smaller than the magnitude of the priming effect. Because the antiprimed objects were identified less accurately than baseline objects (where no priming or anti-priming occurred), it can be assumed that the recognition of these objects is being affected by overlapping representations of the objects they were previously presented with.

Chinese Characters:
A study by Zhang et al. (2017) [30] provided additional evidence of antipriming by investigating the effects of antipriming and priming in a series of Chinese character identification tasks. Their results demonstrated that identification accuracy of old characters (primed) was significantly higher than baseline measurements, however identification accuracy of novel characters was significantly lower than baseline measurements (antiprimed). This can be understood as because the novel characters shared visual aspects of the old characters, however were not familiar, the participants may have automatically been primed to identify these novel characters as the old characters, thus participants had to correct themselves in their identifications, leading to a less accurate and longer identification.

Patients Suffering from Global Amnesia:
A study by Schnyer et al.[31] investigated the effects of antipriming among nine amnesic patients and ten matched controls in order to test whether antipriming could be an effect of memory. Participants engaged in a two part experiment, where in the first part, a baseline measure of familiar object recognition was obtained (uninfluenced by positive priming or antipriming, and against which both priming and antipriming is measured). In the second part, participants viewed an additional set of different visual objects, and after that they were to name that set of objects again, (to measure positive repetition priming) intermixed with another set of new objects (to measure anti-priming). The results were consistent with their hypothesis that antipriming does not reflect influences from episodic memory, as antipriming was found to be intact in patients suffering from global amnesia, therefore the amnesic patients were not impaired in regard to object recognition.

fMRI Evidence:
With functional magnetic resonance imaging, one can use a blood oxygenation level dependent (BOLD) measure to track neural activity. This technique maps the hemodynamic response in different areas of the brain [32].Changes in local hemodynamics (the ratio of oxygenated-to-deoxygenated hemoglobin) are observed as an indirect measure of activity in the brain[33]. The typical finding with fMRI during repetition-priming tasks is a decrease in BOLD signal elicited by repeated items compared against BOLD signal elicited by new or unprimed items[34]. This decrease has been shown in regions of the ventral temporal cortex, medial temporal cortex, and areas of frontal cortex.

Marsolek et al. (2010)[35] also used fMRI to show that strengthening some visual object representations not only enhances the subsequent ability to identify those (repeated) objects, but also impaired the ability to identify other (non-repeated) objects. This results in a weakening of the representations of non-repeated objects, in that those objects elicit increased neural activity in order to reestablish their weakened representations.

Theory of overlapping representations
Visual anti-priming begins with the question of whether the representations of different items are stored in seperate or overlapping manners. Past cognitive models and theories suggest localist/discrete representations where different items are stored with spare traces. (see, e.g., Grainger & Jacobs, 1996; Hintzman, 1986; Jacoby, 1983; Logan, 1990; Medin & Schaffer, 1978; Poggio & Edelman, 1990; Shiffrin & Steyvers, 1997), Other cognitive models suggest that superimposed representations with different items are stored in distributed and overlapping traces (see, e.g., Anderson & Hinton, 1981; Eich, 1982; Knapp & An- derson, 1984; Masson, 1995; McClelland & Rumelhart, 1985; Murdock, 1982; Seidenberg & McClelland, 1989). Visual anti-priming provides evidence for the cognitive models which suggest superimposed reresentations of visual objects and a continual adjustment of repetition priming effects. This is based on neural implementational evidence that suggests that familiar visual shapes are represented in a distributed and partially overlapping manner in ventral temporal cortex. In regard to visual anti-priming this means that viewing an object strengthens those neural connections that aid in its identification, via small representational changes that aid in subsequent identification for that item (repetition priming) (MASKED ANTIPRIMING: A BEHAVIORAL AND EVENT-RELATED POTENTIAL EXAMINATION OF SHORT-TERM ANTIPRIMING EFFECTS) which in-turn weakens the connections of representations of objects that share some representational overlap which have not been viewed recently. These superimposed representations are beneficial to effecient storage and generalization abilities, however they have negative effects in terms of learning new objects (MASKED ANTIPRIMING: A BEHAVIORAL AND EVENT-RELATED POTENTIAL EXAMINATION OF SHORT-TERM ANTIPRIMING EFFECTS)

Visual Anti-priming and Priming
Anti-priming is related to priming which is a repetition effect where identification of an item can be improved due to prior experience with the particular item (repetition priming), or a related item (conceptual or semantic priming). For example, recently viewing a piano typically facilitates an enhanced identification for some period after. Because priming does not require awareness, it is considered an important example of implicit or non-conscious memory (MASKED ANTIPRIMING: A BEHAVIORAL AND EVENT-RELATED POTENTIAL EXAMINATION OF SHORT-TERM ANTIPRIMING EFFECTS) therefore Strengthening one representation after its usage causes priming for that item but also anti-priming for some other, non-repeated items (What anti-priming reveals about priming). Anti-priming is the detriment of this beneficial effect and demonstrates the cost of priming (What anti-priming reveals about priming).

Evidence for Visual Anti-priming
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