Autism and memory

Overview

Autism is a spectrum disorder which presents many challenges to the study of autism and memory function. It is important for researchers to be able to collect data across the spectrum and develop experimental designs to study both individuals with high functioning autism (HFA) and those with moderate-low functioning autism (M-LFA). Methods to classify individuals into one of these groups include intelligence testing, which enables researchers to make methodical comparisons and analyses between HFA and M-LFA individuals. Alternatively, in recent years, “mixed” studies of both HFA and M-LFA participants are done as well.

Some of the earliest references to the topic of autism and memory date back to the 1960s and 70s when several studies appeared proposing that autism should be classified as an amnesic disorder. What is now diagnosed as autism, was formerly diagnosed as developmental amnesia. Subsequent studies had mixed results; some found support for impaired memory, others found evidence of relatively intact memory function. Even though the view of autism as an amnesic disorder of memory has now been rejected, there are still many studies done on the deficits in memory function that are associated with autism. Furthermore, in the memory studies there were observations of memory dysfunctions in autism that were consistent with a deficit in executive functions. Theories have been developed stating that the memory deficits are a reflection of primary deficits in executive function, or of a primary deficit in the processing of complex information.

It has been difficult to get consistent results in autism research. One of the reasons for this is that the autistic population is very diverse, with differences in development and cognitive levels. However, there are a couple of findings that have been replicated in several studies:

Declarative memory and autism

Declarative memory is memory which can be consciously recalled, such as facts and knowledge, for instance autobiographical memory. Within declarative memory is semantic and episodic memory. Semantic memory is facts, and episodic memory is recalling previous experiences in life. Studies on individuals with ASD has shown impairments to their episodic memory but a relative preservation of their semantic memory. The brain regions that play a major role in declarative learning and memory are the hippocampus and regions of the medial temporal lobe. Little research has been conducted on M-LFA individuals and memory function. Memory profiles of M-LFA individuals and of HFA individuals seem to be similar, but there is some evidence that declarative memory impairment is consistently greater for M-LFA individuals than for HFA individuals.

Autobiographical memory

One aspect of autobiographical memory is the self-reference effect, which means that typical people have a stronger memory for information that is relevant to themselves. It has been theorized that individuals with ASD have diminished psychological self-knowledge, but an intact physical self-knowledge. As a result, these individuals show impaired autobiographical episodic memory and a reduced self-reference effect (which may each rely on psychological aspects of the self-concept) but do not show specific impairments in memory for their own rather than others’ actions (which may rely on physical aspects of the self-concept).

Impaired memory binding may also play a role, but more evidence is needed. Individuals with ASD are able to encode events at perceptual and objective levels, but they are unable to encode events in a subjective manner.

A 2012 study conducted by Laura Crane et al., like previous studies, suggests that adults with ASD experienced a reduction in the speed of recall of the autobiographical memory as well as the detail of memory in comparison to typical adults. However, the study results suggest that when adults with ASD were able to retrieve these memories their accounts were qualitatively similar to typical adults.

Prospective memory

The landmark study conducted by Jones et al. in 2010 is the first one to examine evidence-based prospective memory impairment for ASD individuals. The primary findings of this study provide evidence suggesting that poor social and communication skills in ASD individuals have an effect on their prospective memory function.

With these demonstrated connections between social communication skills and prospective memory, several hypotheses have arisen concerning what specific aspects of diminished social skills are influencing prospective memory impairment. Prospective memory relies heavily upon social motivation—like the desire to be socially included, insight and perception into other people’s emotions, and the ability to read social cues. Individuals with ASD are largely tuned out to these types of social motivation, which then affects their prospective memory. Difficulty reflecting upon one’s own mental state and the mental state of others, self-awareness and self-monitoring deficiencies likely also play a role in impaired prospective memory.

A recent study conducted by Altgassen et al. in 2012 also suggested that even though there are differences between individuals with ASD and typical adults when it comes to planning performance and organizational skills, there is no significant difference between individuals with ASD and typical participants when it comes to rule adherence. In fact, ASD individuals tend to follow rules very closely once they have been learned. These findings suggest that everyday organizational task rules are not always evident ASD people, and if they were targeted as rules it would be easier for them to follow. Prospective memory in autism has not been widely studied, so further research needs to be conducted in this field in order to investigate if there is supporting evidence to this claim.

Cued recall

Cued recall, research has been conducted primarily with HFA individuals, but some studies have shown common weakness on cued recall tests for both groups of HFA and M-LFA individuals. In another study, testing a HFA group and a control group of non-ASD individuals revealed that the ASD group made more intrusion errors on recall trials. This evidence also supports the hypothesis that ASD individuals may have a deficit in cued recall. Studies about temporal order memory and ASD participants also indicate that temporal order memory for verbal information is impaired in ASD individuals. However, there is also contradictory evidence for these claims. A 2001 study conducted by Mottron et al. found that ASD individuals, unlike typical individuals, do not benefit more from semantic rather than phonological cues. ASD individuals do not always conform to the Levels of Processing principle, since they benefit the same from deep and superficial recall cues.

In a recency judgment task study conducted by Gras-Vincendon et al., evidence suggested that temporal context memory is not impaired in individuals with HFA. The study proposes this is due largely because the recency judgment task involves more automatic than organizational processing. The researchers proposed that the supposedly impaired temporal order memory for verbal information found in Bennetto’s work is actually due to difficulty with general complex verbal stimuli.

Recognition

Recognition in HFA individuals has been widely studied. Overall, these studies conclude that the majority of HFA individuals have intact recognition ability. Non-social stimuli recognition is often superior, or “robustly intact”, although there is some evidence suggesting that HFA individuals have difficulty with complex scenes and color combinations. For example, HFA individuals exhibit intact recognition of non-social stimuli such as written words, spoken sentences, pictures of common objects, and meaningless patterns or shapes. For HFA individuals impaired recognition have been found in object-location and object-color recognition tests, and recognition of words encoded self-referentially. For more information regarding recognition of social stimuli for individuals with autism, see the face perception page.

Contrary to the plethora of HFA recognition memory studies, the study of recognition for M-LFA individuals is considerably lacking. The studies that do exist predominantly point to impaired recognition of pictures, words to name objects and other non-social stimuli. Four delayed recognition studies reported recognition impairment for M-LFA participants. Additionally, four of the seven primary studies of non-social stimuli recognition revealed significant impairment of non-social stimuli for M-LFA individuals. The other three studies were less reliable because of methodology. Boucher, Lewis and Collis gathered data supporting poor facial recognition, something widely observed for M-LFA individuals.

Implicit/Non-declarative memory

Research suggests that both HFA and M-LFA individuals show strong implicit memory function. HFA individuals display intact implicit memory for non-social stimuli, unimpaired classical conditioning and performance on other implicit learning tasks. HFA individuals displayed normal perceptual and conceptual priming. Studies concerning implicit memory in M-LFA individuals are sparse and further study is needed.

As mentioned above, there are very few reliable studies of non-declarative memory for M-LFA. However, there are some speculations. Some consider that the impaired motor skills evident in many cases of M-LFA may suggest impaired procedural learning. Other studies, including Walenski (2006) and Romero-Muguia (2008), also think that ASD behavior is indicative of implicit memory function. For example, many ASD individuals have exceptional implicit perceptual processing abilities in mathematics, the arts and in musical improvisation. Furthermore, there is speculation that because M-LFA individuals are often characterized by habit and routine, habit formation is likely unimpaired. Behavioral treatments and therapies used with M-LFA individuals are usually very helpful, suggesting that implicit knowledge can be acquired and conditioning is intact.

Neurological

Multiple studies suggest that memory deficit observed in ASD has a biological explanation linked to abnormalities in the hippocampus and other neural regions responsible for strategic regulation, such as the amygdala and the frontal cortex.

Further research

Across the board, it is agreed that there is an urgent need for more research concerning M-LFA memory function. Specifically, there are about half as many M-LFA studies on memory compared to HFA. It should be noted that very few studies of implicit/non-declarative memory exist and almost no brain studies. Almost all of the M-LFA studies are conducted with school-aged children, so there is a great need for a wider age range in memory studies. Very little mapping of the developmental process of ASD has happened, so there is an overall need for longitudinal studies of individuals with ASD across their lifetime. Replication and extension of prospective memory research is needed as well as further cross-sectional and comparison studies for HFA and M-LFA. Recently a specific call has been issued for the investigation of total loss of declarative memory in significantly low-functioning, nonverbal individuals with ASD.