Relationships Between Expertise And Distinctiveness: Abnormal Medical Images Lead To Enhanced Memory Performance Only in Experts Part 1

Abstract

Memories are encoded in a manner that depends on our knowledge and expectations ("schemas"). Consistent with this, expertise tends to improve memory: Experts have elaborated schemas in their domains of expertise, allowing them to efficiently represent information in this domain (e.g., chess experts have enhanced memory for realistic chess layouts). 

Encoding of memory refers to converting information into a form that the brain can understand and remember. Memory, on the other hand, refers to the ability to use and utilize encoded information. The two are inseparable, and the encoding of memory is crucial to improving memory.

How can we carry out effective memory encoding? First, memory encoding requires attention to the characteristics of the information. We should break down the information into multiple parts, and each part should have a clear concept, which helps the brain store the information as a lasting memory.

Second, it is more effective to encode information in our way. For example, you can relate information to a previous experience, or relate it to a situation. These methods can help us understand and store information more deeply.

In addition, pay attention to practicing memory, which is very helpful for improving memory encoding and retention. For example, you can use various memory games to improve your memory skills, such as memory cards, numbers, storylines, etc.

In short, memory encoding and memory are complementary to each other. Only through effective encoding can high-quality memories be formed, thereby improving memory. A positive attitude and practice are the keys to improving memory. Let us work hard to strengthen our memory ability, master more useful knowledge and skills, and lay a solid foundation for the future. It can be seen that we need to improve memory, and Cistanche deserticola can significantly improve memory because Cistanche deserticola is a traditional Chinese medicinal material that has many unique effects, one of which is to improve memory. The efficacy of Cistanche deserticola comes from the multiple active ingredients it contains, including tannic acid, polysaccharides, flavonoid glycosides, etc. These ingredients can promote brain health through a variety of pathways.

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On the other hand, in most situations, people tend to remember abnormal or surprising items best-those that are also rare or out-of-the-ordinary occurrences (e.g., surprising-but not random-chess board configurations). 

This occurs, in part, because such images are distinctive relative to other images. In the current work, we ask how these factors interact in a particularly interesting case-the domain of radiology, where experts actively search for abnormalities. 

Abnormality in mammograms is typically focal but can be perceived in the global "gist" of the image. We ask whether, relative to novices, expert radiologists show improved memory for mammograms. 

We also test for any additional advantage for abnormal mammograms that can be thought of as unexpected or rare stimuli in screening. We find that experts have enhanced memory for focally abnormal images relative to normal images. 

However, radiologists showed no memory benefit for images of the breast that were not focally abnormal but were only abnormal in their gist. Our results speak to the role of schemas and abnormality in expertise; the necessity for spatially localized abnormalities versus abnormalities in the gist in enhancing memory; and the nature of memory and decision-making in radiologists.

Keywords Expertise. Radiology. Recognition memory. Long-term memory.

Our ability to remember information is deeply dependent on our existing knowledge structures, or schemas (Bartlett, 1932; Hintzman, 1986). Even superficially identical information is better remembered if it is integrated into a set of knowledge rather than simply seen as arbitrary. 

For example, people are better at remembering that someone is a baker than that someone's name is Baker because the profession of baker activates a rich set of meaningful associations that the name Baker does not (McWeeny et al., 1987); and people remember visual images better if they recognize them as faces than if identical images are not recognized, but seen as meaningless texture (e.g., Brady et al., 2019). 

Different people have different knowledge and schemas, in part based on their expertise, and this has consequences for memory: Imagine after playing a round of chess, you are asked to recreate the board from some critical moment in the game. 

For most people, this task would prove very difficult. However, if you were a world-class chess player, this might be quite easy. Becoming an expert in a domain such as chess changes our memory for items in that domain of expertise (Chase & Simon, 1973; de Groot, 1946), allowing us to store more information as long as this information is consistent with the expectations we have formed as a result of our expertise (Gobet & Simon, 1996). 

A large literature is devoted to quantifying memory benefits in experts compared with novices (e.g., Ericsson & Kintsch, 1995; Engle & Bukstel, 1978; Gobet & Simon, 1996; Vincente & Wang, 1998). 

For example, car experts can remember more car images in visual working memory (Curby et al., 2009); baseball experts can remember more baseball-related information in long-term memory (Voss et al., 1980); and expert radiologists have better long-term memory for mammograms-but not natural scenes or real-world objects-compared with controls (Evans et al., 2011). 

Why do experts show this increase in memory performance for their domain of expertise? In the literature on expertise, many authors posit that memory improvement occurs because existing knowledge allows experts to know what variation to expect for information in an expert's domain (e.g., Vincente & Wang, 1998). That is, existing schemas make the relevant part of the information predictable and thus easier to encode and remember (Graesser & Nakamura, 1982). 

Thus, in many ways, memory benefits in experts may be considered a manifestation of a broader phenomenon where information that is understood as meaningful-and thus integrated into a schema-is easier to correctly recognize or recall (Bartlett, 1932). 

For experts, there may simply be a wider variety of meaningful concepts and schemas, resulting in a richer ability to understand and remember stimuli in their domain of expertise (e.g., Ericsson & Kintsch, 1995). 

This is sometimes known as an organizational processing account of expertise: experts can have improved memory because they are better able to chunk this information and otherwise create effective knowledge structures (Ericsson & Kintsch, 1995; Rawson & Van Overschelde, 2008). Is better organization the sole reason for better memory in experts? Beyond schemas and knowledge organization, experts in some domains-particularly those where the expertise is more perceptual, like radiologists looking at mammograms or car experts focusing on the details of cars-may have developed specialized processing mechanisms for their domain of expertise that take advantage of the way stimuli vary in that domain. 

For example, experts in some domains employ more holistic processing strategies for objects of their expertise (Bilalić et al., 2011; Gauthier et al., 2000; Gauthier et al., 1999; Richler et al., 2011; Watson & Robbins, 2014). 

Enhanced perceptual expertise may allow experts to process more information about an item even in the same amount of time, and lead to richer memory traces (Ericsson & Kintsch, 1995). In addition to building richer knowledge structures and better perceptual encoding, there is a third factor that could explain experts' improved memory performance in domains of expertise, which has often been overlooked in studies of memory: increased distinctiveness of items when they are items of expertise (Rawson & Van Overschelde, 2008). 

In contrast to views that claim memorability is an intrinsic aspect of a stimulus (e.g., Bainbridge et al., 2013), a significant body of literature argues instead that the critical driver of how memorable an item is in a given context is its distinctiveness from other items currently being stored in memory. Imagine, for example, you are given a list to remember that has 30 animal names and also the word "bread" on it. 

People tend to remember this distinctive word ("bread") most accurately-and this is true even if it appears first on the list, so its unique status is not yet known and it is not differentially attended or processed (Calkins, 1894; Hunt, 2006). Memory models naturally predict this effect because most memory models propose that memory is strongly limited by interference at retrieval, and having more unique features allows easier retrieval (e.g., Shiffrin & Steyvers, 1997). 

This is broadly consistent with the idea that abnormal or schema-inconsistent items tend to be better remembered than expected, schema-consistent items (Friedman, 1979; Hollingworth & Henderson, 2003; Light et al., 1979; McDaniel & Einstein, 1986; Pedzek et al., 1989). 

For example, people tend to better remember unexpected aspects of images (Friedman, 1979). How does such distinctiveness interact with expertise? For experts, many items may be unique from other items in a set in a way that would not be noticed by nonexperts, thus enhancing memory for those items as they would then be more unique in the set for experts than nonexperts (Rawson & Van Overschelde, 2008). 

In summary, experts are often better at accurately recognizing or recalling information in their domain of expertise. This can arise from at least three factors, each of which has been independently studied: experts may have changed perceptual processing strategies; may benefit from general usage of schemas to organize memory; or may benefit from increased distinctiveness of items in memory. 

However, the way these effects interact has rarely been studied, and many have been studied primarily in domains with limited or no perceptual expertise available (e.g., in word lists).

The current experiments: Memory for mammograms in novices and expert radiologists

To understand how expertise affects memory, and how each of these three factors may play a role, the current experiments ask how expertise affects memory for mammograms (comparing novices and expert radiologists), and test whether expert radiologists have better memory for abnormal images (i.e., cancerous mammograms) when compared with normal images (i.e., noncancerous mammograms). 

While for normal mammograms, perceptual encoding benefits, schemas, and distinctiveness all likely play a role in an expert's memory, abnormal mammograms provide a unique case study. Abnormal mammograms do not violate a radiologist's schema (as they are trained to look for abnormalities), but abnormal cases do provide distinctive retrieval cues (e.g., this mammogram has calcifications in this location) which would not be available to nonexperts who have no idea that those little white spots are significant. Nor would these cues be available in normal mammograms. 

Abnormal mammograms therefore present an interesting case; they are schema-consistent, while also potentially providing a unique window into the role of distinctiveness in an expert's memory. To measure memory performance, we will use receiver operating characteristic (ROC) analysis to take into account the possibility of differential false alarms and differential response criterion, which is critical to understanding whether any effects we observe are truly changes in memory strength. 

We predict that experts will have improved performance compared with nonexperts for both normal and abnormal mammograms because of their perceptual expertise and because they have developed schemas over time to represent these complex images. We also predict that abnormal items might show even more benefit for radiologists compared with nonexperts because, for radiologists and radiologists alone, these images have unique and distinctive retrieval cues available. 

We focus on radiologists' memory for mammograms for two reasons: First, the search for signs of breast cancer involves a usefully specific perceptual expertise. For instance, only 2 to 3 kinds of local abnormalities are typically present in abnormal mammograms, and radiologists have significant perceptual expertise whether looking at normal or abnormal medical images. 

Second, there are two senses in which a mammogram might be considered "abnormal": (1) It could contain a focal abnormality. In our study, these are masses or architectural distortions that are subsequently proven to be malignant. (2) Given a mass (for example) in one breast, the other breast could be considered abnormal in the sense that the image comes from a patient with cancer. 

We assess the impact of each of these two kinds of abnormality on memory. Note that a mammogram might be considered "abnormal" if it shows a benign mass. We did not use such stimuli in this study. Radiologists are explicitly trained to recognize an image as abnormal if they detect the presence of a visible, localized abnormality, like a mass or calcification. 

In addition, recent research has shown that, if asked in an experimental setting, radiologists can detect a "gist" of abnormality in the breast contralateral to the lesion. They perform at above-chance levels when asked to categorize images as coming from normal or abnormal patients (Evans et al., 2016). In other words, this study suggests that radiologists do not always need to see a localized physical lesion to know that an image is abnormal. 

This global signal of abnormality is relatively subtle. More importantly, for present purposes, work on this gist signal is new enough that most radiologists are unfamiliar with the concept. Thus, any impact on memorability could be considered to be the result of an implicit effect of abnormality. Published studies of the gist of abnormality have involved giving radiologists only a brief (250–500 ms) glance at an image. While this seems sufficient for expert radiologists to gain some evidence of abnormality, it remains unknown whether this ability impacts radiologists' memory for normal versus abnormal images. 

To summarize, the questions guiding this experiment are the following: Do radiologists show improved memory performance for abnormal images compared with normal images? If so, does global gist produce enhanced expert memory for images of the breast contralateral to the breast that contains focal signs of cancer? Alternatively, does any abnormality advantage in memory depend upon having a focal abnormality that can draw spatial attention? 

Experiment 1 is a baseline study with novice observers, whose performance can be compared with radiologist performance in Experiment 2. In addition, Experiment 1 allows us to determine whether our stimulus set contains images that are memorable regardless of expertise. Experiment 2 assesses memory performance in expert radiologists. 

To anticipate our results, Experiment 1 reveals patterns in our image set that we take into account in Experiment 2. In Experiment 2, we find a large memory benefit for radiologists relative to novices as well as an abnormality advantage in radiologists for focal abnormalities. We find no evidence that experts make use of a nonfocal gist of abnormality either in judgment or memory.

Experiment 1: Novices

Method

Participants

Sixty participants (23 female participants, mean age 38 years) were recruited for this experiment through Amazon's Mechanical Turk, which offers monetary compensation for participation in online tasks. Mechanical Turk workers are reasonably representative of the American adult population (Berinsky et al., 2012; Buhrmester et al., 2011; Difallah et al., 2018), and provide data that are comparable to data obtained when participants are tested in experimental psychological laboratories (e.g., see Brady & Alvarez, 2011, for a comparison in a visual memory context). 

All participants gave informed consent, were compensated at a rate of approximately $10/hour, were located in the United States, and had a hit approval rate greater than 95%. Informed consent procedures were approved by the Institutional Review Board of the University of California, San Diego.

Stimuli and procedure

Participants viewed single breast mammograms in this study. The stimulus set consisted of 80 abnormal (cancerous) cases and 40 normal (noncancerous) cases. All images were unidentified. 

All images were classified by a group of trained radiologists who did not participate in the study. Normal images were noncancerous and did not contain benign lesions. Abnormal images consisted either of histologically verified malignant masses or architectural distortions (see Evans et al., 2016, for a more detailed description of this stimulus set). Half of the abnormal images contained a visible abnormality (i.e., a lesion was present) and half were images of the breast contralateral to the breast with the lesion (i.e., still an abnormal case, but with no focal indication of that abnormality). 

Thus, the entire set consisted of 40 normal images, 40 focal-abnormality images (herein referred to as abnormal), and 40 non-focal abnormality images (images contralateral to the breast with the focal abnormality), herein and henceforth referred to as contralateral-abnormal. Each image subtended approximately 16 × 20 degrees of visual angle at an estimated viewing distance of approximately 60 cm from the screen. 

On each trial, one image was present for 3 seconds, followed by a new screen containing response questions. The mammogram was randomly chosen to be either normal, abnormal, or contralateral-abnormal. Critically, each image was also either a new image (presented for the first time in the experiment) or a repeated image from 3 trials back or 30 trials back (3-back and 30-back, respectively). 

Of the images that were later repeated, 50% were repeated at 3-back, and 50% were repeated at 30-back. The experiment was balanced such that ~20% of trials in the first and second half of the study were 3-backs and 30-backs, respectively. 

In fact, due to sampling different streams of images for each participant, in our exact pool of radiologists, 18% of trials were 3-backs in the first half of the trials, versus 23% in the second half of the trials, and 22% were 30-backs in the first half of the trials, and 20% in the second half. In total, with repetitions, there were 210 trials: 120 new images (40 per condition), plus 90 repeat images (30 per condition, split evenly between 3-back and 30-back).

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