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Sentence Comprehension Deficits in Alzheimer’s Disease

Most people know that there are extreme cognitive deficits associated with DAT, otherwise known as Alzheimer ’s disease, but what is the nature of these struggles? What do those with DAT have the most trouble on, and what is the biggest cause of the troubles? It turns out that those with DAT have the biggest deficits in attentional tasks, and a lot of their memory issues stem from an inability to focus and maintain attention. In 1998 “Sentence Comprehension Deficits in Alzheimer’s Disease: A Comparison of Off-Line VS. On-Line Sentence Processing” looked at and tried to analyze the reasons behind memory deficits in DAT individuals.

The experimenters wanted to test whether the problems were stemming from a lack of syntactic knowledge, or the knowledge of how words form into sentences correctly, or from a working memory deficit. Working memory is the system that holds information in short term memory, deciding whether to attend to it, rehearse it, and transfer it into long term memory or to just throw it out. The better a person’s working memory, the better they can learn and pay attention to what they are looking at. They decided to test this idea through the use of on-line and off-line tasks. On-line tasks are when the participant is only doing one thing, in this case simply deciding whether the sentence was grammatically correct, as quickly and accurately as possible. Off-line tasks are the same, except that the participant has to do two things at once. They must also name the word while deciding whether the sentence it is in is grammatically correct. This requires a lot of working memory ability to switch attention between these two tasks and do both well. If the DAT older adults did significantly worse than normal older adults on the simple on-line task and also on the complex off-line task then that would mean they were having a lot of trouble with syntactic knowledge; they can’t figure out what the heck the sentence means even when they aren’t distracted. If, on the other hand, they only perform poorly on the complex off-line task it means that they do not have trouble with syntactic knowledge, they can figure out the sentence fine. Instead this means that DAT subjects are having a difficult time focusing their attention and doing both tasks when compared to the healthy older adults.

They found strong evidence of working memory difficulties in the DAT individuals. They had no noticeable difficulties on the simple on-line task, but when required to do two things at once they fell apart, often so focused on one aspect of the test that they could not do the other at all. This makes a lot of sense when looking at Alzheimer’s research. Attentional deficits are prominent, often showing up long before any memory difficulties. One longitudinal study looked at the Stroop Task, a test where a person is presented with words in various colors. They must say the color and not the word, simple right? Except that on 1/3 of the tests the word is the same as the color, i.e. “BLUE” is presented in blue (congruent trials), on one third they are different, i.e. “BLUE” is presented in green (incongruent), and on one third they are unrelated, i.e. “BIRD” is presented in red (unrelated). People read things automatically, and so it is often extremely difficult to say the color of the word when the word itself is a different color (incongruent trials). This is a good test of attentional control. Many participants in this study took the Stroop Task, some of them had DAT and some were healthy, and they found that in general those with DAT had extreme difficulty on incongruent trials, showing breakdowns in attentional control. The most interesting part, however, is that years later they went back and found all of the participants. Many of the healthy group had developed DAT. When they went back and looked at their Stroop Task results from the original experiment the results looked exactly the same as those in the DAT group. They were showing the exact same detriments in attention years before they showed any outward signs of DAT at all.


Kempler, D., Almor A., Tyler, L.K., Andersen, E.S., MacDonald, M.C.. Sentence

              Comprehension Deficits in Alzheimer’s Disease: A Comparison of Off-Line VS. On-Line

              Sentence Processing. Brain and Language. 64 (1998).

David A. Balota et al. Predicting Conversion to Dementia of the Alzheimer’s Type in a Healthy

              Control Sample: The Power of Errors in Stroop Color Naming. Psychology and Aging

              25(1) (2010).

  1. March 19th, 2014 at 21:35 | #1

    This is a very interesting way to think about Alzheimer’s disease, since most people typically think of it as strictly a problem with memory. This study, along with the Stroop Task study, gives a new perspective into the nature of this disease. From personal experiences, it seems as if Alzheimer’s patients lack syntactical understanding as well, so it is extremely interesting that this study isolates the deficits to attention. Ji Won Song, in her post Pay Attention, Grandma! also mentions this failure in ability to control attention as we age, which is interesting in contrast to the Stroop Task test on individuals with Alzheimer’s. I am currently taking a cognitive psychology class, in which we also discussed the significance of the follow up study between the adults who developed Alzheimer’s and those who did not. I find it curious that the adults who did not develop Alzheimer’s perform similarly to the young participants. This would contradict the study in Song’s post. It would be interesting to see if the study in Song’s post may have results similar to the Stroop Task if there was another study between the older adults who develop Alzheimer’s and those who don’t. Then there would be more evidence demonstrating that attention control is defective in Alzheimer’s patients, and also be another early predictor of individuals affected by this disease, much like the Stroop Task.

  2. March 20th, 2014 at 21:09 | #2

    Going off of Emily’s post, I too think it is extremely interesting that the adults who developed Alzheimer’s disease were abnormally inhibited in their original incongruent trial on the Stroop Task, fourteen years prior to developing the disease. In the original test, the healthy adult group overall performed well on the Stroop Task; however, when the researchers divided the original healthy adult group’s data in half, separating individuals who developed DAT fourteen years later and those who did not, participants who developed DAT were abnormally inhibited by the incongruent trials, showing that it is possible for the Stroop Task to determine who is likely to experience DAT later in life. I think this ability to see the disease through its attentional deficits years before the memory impairments show is extremely interesting in regards to the two types of Alzheimer’s disease, early onset and late onset. Early onset DAT is very rare, affecting individuals between the ages of 30 and 60. It is inherited in a Mendelian fashion, or following classic Mendelian inheritance laws, and therefore can determine who is likely to develop the disease and who carries alleles for it. Late onset DAT on the other hand is very common and becoming increasingly prevalent now that humans are living longer. Late onset DAT does not follow a clear inheritance pattern, making it extremely hard to predict who is likely to develop Alzheimer’s. Researchers have discovered risk factor genes, which have particular alleles that somewhat increase the likelihood of an individual getting late onset DAT; yet, many people who do not carry any of these alleles still develop DAT. One risk factor gene is APO4e, which causes amyloid plaques to form in the brain. These protein plaques interfere with the synaptic connections between neurons, progressively reducing the brain’s functions. Nevertheless, it is evident that amyloid plaques are not the only factor causing the brain’s functional degeneration (Halpern). I think it would be extremely interesting and potentially helpful to look at the Stroop Task in regards to the two types of Alzheimer’s disease, particularly focusing on whether individuals who developed late versus early onset DAT performed differently prior to their clinical dementia rating (CDR) showing any form of disease development. This could be a potential way to see if there are any obvious differences between individuals who inherit early onset Alzheimer’s and those who develop late onset Alzheimer’s; as well as to determine whether the formation of late onset DAT can be predicted to some degree by the Stroop Task.

    Sue Halpern, Annals of Medicine, “The Gene Hunters,” The New Yorker, December 12, 2005, p. 84

  3. March 20th, 2014 at 22:58 | #3

    This post is very interesting, as I too have a family member with Alzheimer’s disease. My grandma has pretty advanced Alzheimer’s and when I visited her in Japan, I was amazed to see the difference in her in just a few short years. Watching her from a psychology perspective, I was very interested to see how her attention span was functioning. When conversing, she seemed present and seemed to understand the content, but her memory was stuck in the past. She forgot she had grandchildren and mistook me for her sister-in-law that had already passed. What was most bizarre though, was the fact that about every twenty minutes or so, she would kind of withdraw from “reality,” like someone switched her off-button. When she would “wake back up,” it was like she was a blank slate. A picture that we showed her a mere ten minutes ago would capture her attention again, like she had never seen it before. She would ask the same question she asked six minutes ago, and we would have almost the exact same conversation again. The reason this study interests me so much, is because of the multi-tasking idea. My grandma could converse normally, but when she was eating dinner or watching tv, she couldn’t do another thing simultaneously. The fact that it took her that much effort to focus on one activity really shows how important our working memory is in basically everything we do. In my cognitive psychology class we have discussed how necessary it is, for long-term memory especially, to attend to things that we want to encode, and successfully store them for use later. Kempler et al.’s 1998 study invites real insight into many precursors to actually showing the signs of Alzheimer’s disease. If we can study more closely how the working memory can be at a deficit, then we may be able to treat this disease earlier. Maybe there is a chemical in the brain that either starts to get produced less, or more, that affects the memory portion of the brain. Maybe structures start growing in the brain, kind of like a tumor, that can interfere with the way the brain communicates, and stops the flow of incoming information. Maybe it is something wrong with the corpus callosum, where they can do one task because it is only processed in one part of the brain, but once they start two tasks, they can’t process the second because the information is not reaching the other half of the brain–the communication is lost. I think it is good to look at this study in conjunction with the Stroop Task because it reasserts the previous study, showing that the ability to stop one process from happening in the face of another is difficult for those with the disease. This shows that doing two things at once, processing the information while simultaneously switching to a different track of attention, is tough.

  4. December 3rd, 2014 at 22:40 | #4

    I thought you made a very clear connection between cognitive deficits in dementia patients and attentional control. Going off on Emily’s post, a person who has little knowledge of cognitive psychology would probably assume that dementia mainly concerns declines in memory, but would not understand why these deficiencies occur or how dementia goes beyond the need to remember. The Stroop Task is a perfect example of how adequacy in a task does not depend on memory, but rather control over shifts in attention. An example involving dementia patients (that requires both memory and attentional control) concerns a study on false memories (Balota et al., 1999). When participants with and without dementia were asked to recall items previously listed (i.e. BED, REST, TIRED), attentional control was needed to inhibit the critical (yet not-previously listed) item of SLEEP. Dementia patients compared to adults of matching age were shown to have higher rates of false memories, therefore a breakdown in their attentional control. This inability to inhibit the critical item is similar to the Stroop Task described in your post – in both cases, dementia patients could activate items that require automatic processes, but lacked the inhibition of the false memory (for the Stroop task, inhibiting the reading of the word). Your post also reminds me of paper we recently read for class on cognitive advantages and disadvantages for bilingual individuals (Bialystok & Craik, 2010). Through numerous studies, it has been supported that bilinguals are better in inhibiting irrelevant information in Stroop-like tasks. In context to the Stroop task in your post, bilinguals would have a better chance at inhibiting the automatic process of reading the word when it’s time to name the color. This advantage in attentional control has shown to have life-long benefits, including a later onset of dementia. When examining monolinguals with dementia versus bilinguals with dementia, bilinguals tend to show an onset of dementia 4 years later than monoglinguals (Bialystok, Craik, & Freedman, 2007 as cited in Bialystok & Craik, 2010). Like your post, these examples support that dementia not only affects memory, but also a wide range of cognitive abilities such as attention-shifting and controlled processes.

  5. December 2nd, 2015 at 14:17 | #5

    This post is both engaging, and is also very useful in understanding this disease. The way in which you described the Stroop Task and the performance of individuals with Alzheimer’s on that was very clear and concise, and the amount of attentional control that is required to inhibit the automatic reading process is made evident. I also appreciated how the post ended with the connection regarding young individual’s scores on the Stroop Task before they were ever diagnosed with Alzheimer’s, (or ever started showing signs). It is very telling that those young individuals who later developed Alzheimer’s has very low young adult scores in comparison to those who did not develop the disease. I would love to read about more research regarding early signs of Alzheimers.
    Reading this post made me think about deficits in other varying types of memory that those with Alzheimer’s Disease are challenged with. In one of my courses, we learned that individuals with Alzheimer’s also exhibit detriments in their episodic memory. Parallel to this, there are also individuals who experience Semantic Dementia. These people have trouble recalling words. Say someone with Semantic Dementia is trying to tell you a story in which they fell off of a chair. They might be telling the story just fine, until suddenly, they try to remember the word to describe what they were sitting on. They simply will not be able to recall the word, “chair.” One of the ways in which episodic deficits and semantic deficits can be displayed is through either a picture naming task (during which participants are presented with random pictures and they simply point to the image and say what it is), or through a forced choice recognition test (during which participants are first shown an image, then this image disappears, and three other images appear after a delay. The participant has to choose which image out of the three they were presented with beforehand.) Participants with Alzheimer’s and with Semantic Dementia were subjected to both kinds of tests. Individuals with Alzheimer’s dd very poorly on the forced choice recognition task, because they had weak episodic memory, and could not remember which item they had seen previously. Those who suffer from Semantic Dementia did poorly on the picture naming task, because they simply had difficulty generating the words that match with the images. By conducting these two types of tests together, and seeing the deficits in these two separate types of memory, we can deduce that there are indeed memory systems that work independently of each other!

    I wonder what other kind of connections can be made between episodic, working, and semantic memory! Would those who have Alzheimer’s show deficits in all three areas if they are compared with individuals who do not suffer from any kind of memory deficiency? Or, would they just show deficits in some areas of memory and not others? This would be an interesting question to further inquire about!

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