Negative Priming

Pens. Initially, the person picks out the red pen and therefore it is the prime target while the remaining pens in the holder are considered to be prime distractors. When the person wants to use the blue pen (probe target) instead, negative priming effects are observed as the blue pen was previously ignored as the prime distractor.

Negative Priming is the implicit memory effect in which prior exposure to a stimulus unfavorably influences the response to same stimulus at a later time. It falls under the category of Priming, which is a memory effect in which exposure to a stimulus influences response to a later stimulus without any conscious awareness. Negative priming is the phenomenon where a reaction to a stimulus that is previously ignored is slow and error-prone.^[1] For example, when trying to pick out the red pen from the pen holder, the red pen is paid selective attention while the remaining pens are blocked as distractors in some fashion. If the person was to switch to the blue pen, there is a momentary delay in this action. This slow and impaired reaction is called the negative priming effect. Researchers have wondered the cause of this effect and tried to establish some theories and characteristics of negative priming.

Negative priming is believed to play a crucial role selective attention processes and in memory retrieval. Both attention and memory are similar in that many concepts are activated simultaneously and only certain concepts are selectively attended or entered as short term memories. Negative priming is assumed to reflect both the excitation and inhibition associated with the competing distractors during the selection process. While excitation is known to facilitate attention, distractor inhibition model considered the dual mechanism involving excitation and inhibition to be more efficient in selective attention.

Negative priming is also known as the mechanism using which we apply inhibitory control over cognition by selective attention. This does not mean inhibiting all the irrelevant stimuli but just those stimuli that can interfere with the current short term goal or response.^[2] The effectiveness of selective attention depends on the cognitive control mechanism as the load of perceptual distractor processing increases with the increase in load of working memory. Increased load of perceptual processing requires more time and produces the delayed reaction time. Therefore, negative priming effect is the result of this increasing load and therefore depends on the availability of the cognitive control resources.^[3]

Theories and Models

Distractor Inhibition model

Distractor Inhibition model explains the negative priming effect as the result prior inhibition of the stimulus as a distractor in order to facilitate the selection of the target. When the distractor stimulus becomes the target, the response is subsequently hampered due to residual inhibition.^[4][5] This selection of a target refers to selective attention or the ability to respond to a specific object when other objects also compete for a response. While excitation is known to facilitate attention, distractor inhibition model considers a dual mechanism involving excitation to boost target signal and inhibition of distractors to be more efficient in selective attention. A dual mechanism includes excitation to boost target signal and inhibition of distractors is proposed as the most efficient process in selective attention. This inhibition is triggered when there is a mismatch between a target template and a distractor stimulus and this disparity suppresses the activity. Inhibition of the distractor’s internal representation functions to facilitate selective attention and decays gradually when the external input is no longer present. When a distractor stimulus is re-encountered as the target, the internal representation of this stimulus may continue to be suppressed due to residual inhibition or the inhibition feedback may reactivate and produces the negative priming effect. This resulting impairment of processing an appropriate response to the new target stimulus is observed by the greater reaction time.^[4][6]

There are a few problems associated with this early inhibition model. This model accounts for negative priming only for the stimuli that were first ignored repetitively as distractors. Negative priming effects are justified only under conditions of goal directed behavior of selectively attending to a stimulus while inhibiting the other competing distractors. Another issue is that negative priming effects have been found to be long-term compared to transient residual inhibition as proposed by this model. There is evidence for long term negative priming effects for as long as 7 seconds.^[7] Long-term negative priming effects have been confirmed by various research and is one of the main concern in this model. Long-term effects suggests that the memory retrieval of the previously ignored distractor creates the negative priming effect rather than residual inhibition.

Following the rise of these issues, Tipper and Houghton modified the distractor inhibition model to account for the negative priming effects over long periods of time. Initially, inhibition process was thought to be a forward view of negative priming as inhibition occurs during the prime trial and negative priming effects are seen in the probe trial. However, this was modified in the Houghton-Tipper Model, in which the probe target stimulus cues the retrieval of the prior inhibition. During the probe trial, the internal representation of the distractor being inhibited would be retrieved and lead to negative priming. This model further suggests that inhibition is a bi-directional process with initial inhibition during selective attention and inhibition during the retrieval process.^[4]

Episodic Retrieval Model

The Episodic Retrieval model theorizes that each encounter with a stimulus is encoded and stored separately as an individual episode. Each episode includes perceptual details of both the stimuli and the response developed for that stimuli. When a stimuli is encountered the second time, the first episode of the stimuli is retrieved aumatically. Simultaneously, an analytical approach of computing a response to the stimuli is also being processed. The probability of the faster method of the to approaches determines the negative priming effect. When the repetitively ignored distractor stimuli becomes the target, the tag associated with the response to that stimuli is also retrieved. This tag associated with response to a distractor will likely be "do-not-respond" tag as opposed to "respond". Retrieval of such a tag presents a conflict between the previous distractor information and the current target information with the need to respond. This conflict requires more time to resolve and this is observed as greater reaction time and is called negative priming effect.^[1][8]

This model has gained more popularity over the last decade compared to the Distractor Inhibition model due to its account of long term negative priming effects. This model does not include any inhibitory mechanism but rather the conflict between the retrieved information and current course of action. The main distinguishing factor between these two models is that the inhibition model occurs during the encoding of the distractor stimuli where as episode retrieval claims that the negative priming occurs only when the memory of the stimuli is retrieved. Essentially, these models vary by their forward view of negative priming as a process inn selective attention and backward view of episode retrieval.^[9] Empirical evidence supporting the Episode Retrieval model comes from studies that determined the decay of negative priming effects as a function of RSI. Episode Retrieval model explains these results in terms of the ability to retrieve an episode based on the ratio of 2 consecutive trial intervals of prime and probe. When the most recent interval is short and the initial interval is long, there is maximum decay in the negative priming effect. However, when the interval of both trials are the same, no decay is found. These show that the negative priming effect is produced by the retrieval of that episode.^[1][8][10] Recent findings lean towards this model but the model itself is not entirely complete. This model lacks in its explanation of how the retrieval of the initial episode creates the longer reaction time. The “do-not-respond” tag is vague and needs more concrete evidence to support this model.

Feature Mismatch hypothesis

This theory proposes that negative priming effect is the result of interference due to the target being located where the distractor was once located.^[1] This theory originated from the findings that selection of a target is not enough to cause negative priming effect, which were observed from experiments where the subjects arbitrarily chose the target out of two possibilities. Feature Mismatch hypothesis is based on the findings of facilitation when the target and location remain same and inhibition when there is a mismatch in the target and its location. This theory may explain the effects of location specific negative priming but lacks in its explanation of negative priming when location is not involved.^[11]

Rather than a complete theory that explains negative priming, it only offers more loop holes in the Distractor Inhibition model. This theory mainly differs from the distractor inhibition model in its stand that selection of a target stimulus where the distractor is ignored is not necessary for negative priming. This theory also provides evidence that negative priming is not restricted to cases of selective attention.^[11]

Temporal Discrimination model

Temporal Discrimination Model attempts to blend in both the selective attention and memory retrieval aspects of negative priming in a less complex model. It is based on the assumption that negative priming is caused only at the moment of response to a stimulus that was previously considered distractor.^[12] This model explains negative priming as the delayed response due to confusion in classifying a stimulus as old or new. A new stimulus is immediately classified as new and undergoes perceptual processing. A repeated old stimulus is is familiar and cues the automatic retrieval of the prior episode. A stimulus that has been repetitively ignored prior to becoming the target is neither entirely new nor old and falls under the gray area. This "gray area" ambiguity slows down the processing of the stimuli. The temporal discrimination model points to this ambiguity as the cause of slowed categorization of the stimulus leading to negative priming effect. Like feature mismatch hypothesis, this model also claims that negative priming is not due to selective attention to the prime target and inhibition of the distractor. This model argues that "negative priming is an emergent consequence of a discrimination process that is inherent to memory retrieval". Temporal discrimination model explains negative priming without reference to inhibition of distractors or the "do not respond" tag and by simple discrimination of "old", "new" and "in between" categories.^[12]

Characteristics of Negative Priming

Stimulus Modality

The primary two stimulus modalities used for negative priming research are visual and auditory stimulus materials. The stimulus presented varied from objects or symbols in visual field to human voices or artificial sounds. Stronger negative priming effects are found for auditory stimulus but the standardized effect sizes between the modalities did not vary.^[1] Evidence for negative priming has also been found across various modes of response including vocal naming, manual key press, and reaching.^[2] Negative Priming was observed for various types of judgement such as identification, categorization, matching, counting and localization. The tasks include:

Stroop Color-Word Task

This task was one of the earliest task that helped identify the negative priming effect. In this task, words that denote incompatibility with the colors in which they are presented are displayed as prime. The color of the prime word is then presented as a probe word in a different color. Subjects are asked to name just the color in which the word is presented and are expected to ignore what the word says. For example, the prime word "green" is shown in BLUE color and then the probe word "red" is shown in GREEN color. Subjects have to name the word "GREEN" correctly during probe trial even though they had to ignore the word "green" and say BLUE during the prime trial. This task utilizes the stroop effect to identify negative priming effects. The distractor suppression effect was obtained with any type of response modality.^[2]

Lexical Ambiguity Task

This task utilizes semantic knowledge of the subject and tests the subject ability to remember the multiple meanings and uses of one word. For example, the word "bank" has multiple meanings and can be referred in different contexts such as "bank is a place where money is deposited" or "banks of a river". The prime target is presented in one context while the probe is presented in any context in which the word can be used. Higher negative priming effects are observed when the the context in the probe trial varies from the prime target. this also provides some evidence of endogenous negative priming, where there is an internal selection of the target among multiple possible association of the same word.^[2]

Identification Task

Identification tasks presents a set of images, sounds, words, symbols, or letters and require the subject to select the prime target based on the location or color with the other being the distractor. The subject will be immediately asked to respond to the probe, which may be a random stimuli, the distractor or something relating to the distractor. Following the probe trial, the subject will be asked to identify the prime target. Certain word naming tasks found negative priming only when probes were presented to the left visual hemifield. This rises the question of the differences in the two hemispheres with respect to negative priming and possible special inhibitory roles of the right hemisphere.^[2]

Matching Task

Subjects will be asked to respond “same” or “different” by matching the target letters or shapes with the explicitly specified goal while ignoring the distractor. Negative priming is found when the target shape or letters was recently ignored as the distractor.^[1]

Localization Task

A table with four arrays, target symbol and distractor symbol are presented to subjects. The goal is to respond by pressing the key that corresponds to the location of the target symbol in the array. Negative priming is shown by the slower responses when the probe target appears in the same location as the distractor during the prime trial. This type of localization task is especially used to test the Feature Mismatch hypothesis as it provides evidence for negative priming during the mismatch of the location and target stimuli. As this task also requires hand motion towards the array in which the target is located, negative priming in this task is action centered.^[11][2][13]

Prime, Probe and Interference

Prime trial is the initial presentation of stimuli that may be repeatedly displayed and/or ignored before the actual testing for the stimulus. Both the target and the distractor are presented during the prime trial. The subject is instructed to identify the target based on the color or other form of identification. Probe trial is the actual testing during which the response is used to measure the negative priming effect. Some experiments may use different forms of interference such as changes in the position of the stimuli (flanker or wobble) or the presentation of completely irrelevant stimuli.^[2] Probe interference is negative priming effect caused by the presence of distractor stimuli present in the probe itself. Probes that did not require the selection of the target over the distractor had a lower negative priming effect. This is being used as counter evidence for the Distractor Inhibition theory as it would need a distractor in its probe to test the inhibition of the distractor.

RSI Effects

Response-Stimulus interval (RSI) is the time difference between the response to prime target and the onset of probe trial stimulus. Negative priming effects are observed for delays of 20 ms to 8000 ms between the prime and probe by various experiments, during which negative priming decays rapidly.^[2] However, a fixed interval or rate of this decay has not been established due to contradicting results from various experiments.^[8][14] This decay has been taken into account by the two both the Distractor Inhibition model and the Episode Retrieval model and use varying results to explain the delay as a part of the model of negative priming. Further research is needed to determine concrete RSI data and establish short-term and long-term negative priming limits.

Conclusion

Among the four theories, the Feature Mismatch hypothesis and the Temporal Discrimination model lack adequate evidence to support them and only incorporate the other two models in some fashion. For example, the Feature Mismatch hypothesis and the Temporal Discrimination model can be easily incorporated into Distractor Inhibition model and Episode Retrieval model respectively. The Distractor Inhibition model was most popular and dominant model until recent contradicting findings pointing to a retrieval mechanism in negative priming.^[1] Episode Retrieval model is gaining more support for the memory based negative priming but lacks in its concrete explanation of the association tags. Perhaps, further research exploring both these models might pave a way to better understand the role of negative priming in both selective attention and memory.

See also

• Priming (psychology)
• Inhibition of return
• Attention
• Working Memory

References

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10. ^ Neill, W.T., Valdes, L.A. (1992). Persistence of negative priming: Steady State or decay? Journal of Experimental Psychology: Learning, Memory, and Cognition, 18, 565–576.
11. ^ ^{a b c} Park, J., & Kanwisher, N. (1994). Negative priming for spatial locations: Identity mismatching, not distractor inhibition. Journal of Experimental Psychology: Human Perception and Performance, 20, 613–623.
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