William James famously said that the world is “one great blooming, buzzing confusion” to an infant whose sensory apparatus is “assailed by eyes, ears, nose, skin, and entrails at once.” As adults, we continue to be assailed by stimuli, but out attentional apparatus permits us to deal with the blooming and buzzing confusion quite well.

We recognize threats in the environment, such as venomous cucumbers, and conversely, we can filter out irrelevant information, such as the annoying invitations to present one’s latest paper in particle physics at a conference on food & nutrition in Kuala Lumpur.

The ability to filter out irrelevant information is particularly crucial if it is intermixed with information that is relevant, such as the email from the Psychonomic Society about the forthcoming meeting in Amsterdam (10-12 May 2018).

How does this filtering take place? Do we just inhibit the processing of information that puts “particle physics”, “nutrition”, and “Kuala Lumpur” in the same sentence? Or do we also selectively facilitate the processing of information that contains the words “Psychonomic Society”?

Recent evidence from neuroscience suggests that participants can selectively enhance the firing of neurons that have a preference for a designated target (e.g., the “Psychonomic Society cells”) and can independently inhibit or suppress those that encode the non-target (e.g., the “junk conference cells”).

A recent article in the Psychonomic Society’s journal Attention, Perception, & Psychophyics explored the idea of inhibition further using a rapid serial visual presentation (RSVP) paradigm. In an RSVP paradigm, participants look at a continuous presentation of visual items which is around 10 items per second, all of which are presented in the same location. RSVP can therefore mimic reading without requiring any eye movements—you simply process the material that appears in the same location in rapid succession.

Researchers Li, Neumann, and Chen used RSVP to investigate a phenomenon known as “negative priming” (NP). The idea behind negative priming is that a stimulus that is a distractor on one trial (the priming trial) becomes the target in the next trial (the probe trial). For example, consider the sequence of events in the figure below:

The participant’s task is to report the identity of the black digit on each trial (i.e., the sequence of events prefixed by an “@” symbol for ½ second). All other events (i.e., letters and red digits) are distractors and are to be ignored.

Note that the target on the second trial (the black 4) was a distractor previously.

Now compare this setup to another sequence of trials, shown in the next figure:

Things are subtly different now, because the distractor digit from the first trial (the red 4) is not repeated on the next trial. Instead, the target on the second trial is a black 6, not shown before.

Perhaps unsurprisingly, the first condition leads to slower responding on the second trial compared to the second condition. The fact that participants had to ignore the red 4 (when it was a distractor) makes it harder to respond to the black 4 (when it is a target). This slowing in responding is the indicator of negative priming.

Li and colleagues used this procedure in a number of experiments to examine the conditions under which distractor inhibition (and hence negative priming) is found.

The first experiment served to establish a baseline for negative priming and confirmed that participants took longer to respond to a probe when the same digit had been a distractor just before, compared to the control condition in which the probe digit was novel. The size of the negative priming effect was modest (between 17 ms and 33 ms, depending on details of the statistical measure) but it was significant.

In the second experiment, the targets (and distractors) interchangeably consisted of number words (e.g., “THREE”) or digits (e.g., “3”), such that the form of the stimulus differed between its occurrence as a prime and a probe. Would the distractor “THREE” inhibit responding to the target “3”? Li and colleagues found a small negative priming effect, suggesting that people inhibited not a physical stimulus but the underlying concept of the number 3.

In a final experiment, Li and colleagues extended the idea of changing the form of stimuli to using different languages, as shown in the figure below. Participants were Chinese-English bilinguals whose first language (L1) was Chinese and whose second language (L2) was English.

The top and bottom panels in the preceding figure differ only in the directionality of the switch between languages. Whereas panel a used Chinese distractors (the character in red, a representation of the number 4) followed by English targets (the black number words), the reverse was true in panel b.

Would negative priming be observed across languages as different as Chinese and English?

Consistent with previous results reported in the literature, participants showed negative priming only in the L1-to-L2 trials (i.e., panel a in the above figure), but no evidence of negative priming was observed when the prime distractor was in L2 and the probe target in L1 (panel b).

Li and colleagues suggested that this asymmetry reflected differences in activation level between the two languages. By definition, participants were more fluent in L1 than in L2. Consequently, when the prime distractor was in L1, strong inhibition was required to prevent it from interfering, and a strong negative priming effect resulted when that inhibition was stimulus-inappropriate for the subsequent probe. By contrast, an L2 prime distractor would be activated relatively weakly, leading to weak inhibition that resulted in negligible negative priming.

Taken together, the results across all experiments are seemingly best explained within a distractor-inhibition framework. As Li and colleagues put it:

“According to this account, [negative priming] is a by-product of the target selection process, during which the representation of the distractor is inhibited. Depending on the task, the inhibition can occur at a physical level or at a semantic level, and the degree of inhibition can be automatically adjusted in response to the potency of the distractor interference via feedback mechanisms. When the distractor in the prime trial becomes the target in the probe trial, the processing of the target is delayed relative to a new item. This can be caused by the lingering inhibition of the previously suppressed stimulus representation, …, or by the inhibitory processes associated with the stimulus, whose appearance as a probe target can trigger the retrieval of its prior processing episode in which the representation of the stimulus was inhibited.”

What is perhaps most remarkable is that this distractor inhibition is applied not to the physical stimulus but to the underlying concept—thus, “THREE” can inhibit “3” as much as a “3” does.

Psychonomics article focused on in this post:

Li, L., Neumann, E., & Chen, Z. (2017). Identity and semantic negative priming in rapid serial visual presentation streams. Attention, Perception, & Psychophyics, 79, 1755-1776. DOI: 10.3758/s13414-017-1327-4.