Bottom-Up and Top-Down Processing in Autism: What Research Suggests

Autistic people often describe experiencing the world in ways that feel different from those around them. This can include noticing details that other people miss, finding some sensory environments overwhelming, needing more time to make sense of a situation, or preferring information to be clear and explicit.

One way researchers have tried to understand some of these differences is by looking at bottom-up and top-down processing.

These terms describe two ways in which the brain makes sense of information. They are not separate systems, and they are not exclusive to autism. Everyone uses both. Research has explored whether some autistic people may place a different balance of emphasis on incoming sensory information, local detail and prior expectations.

The evidence is more nuanced than saying that autistic people are bottom-up thinkers and non-autistic people are top-down thinkers.

What is bottom-up processing?

Bottom-up processing starts with incoming sensory information. The brain receives information such as sights, sounds, touch and movement and builds an understanding from that information.

For example, when entering an unfamiliar room, someone may first notice individual features such as the lighting, the layout, background noise and where people are sitting before forming an overall sense of the situation.

Bottom-up processing is a normal part of perception. It allows us to respond to new information rather than relying entirely on what we already expect to find.

What is top-down processing?

Top-down processing involves using previous experience, knowledge, context and expectations to help interpret incoming information.

If you walk into a familiar office, you are unlikely to consciously process every object in the room. You already know broadly what an office looks like and what normally happens there. That existing knowledge helps you interpret the situation efficiently.

Bottom-up and top-down processing normally work together. The research question is whether the balance between them may differ in some autistic people or in some types of task.

Why are these ideas discussed in relation to autism?

Researchers have long explored whether autistic people show differences in the way local detail and overall meaning are processed.

One influential account was the weak central coherence theory. Earlier versions focused on difficulty integrating information into a global whole. Later work placed greater emphasis on a possible preference or bias towards local, detail-focused processing rather than a simple deficit.

A major review by Francesca Happé and Uta Frith concluded that a detail-focused processing style had support in the autism literature, while also noting that it should be understood as a processing bias rather than a universal inability to understand global meaning.

A later meta-analysis by Van der Hallen and colleagues combined 56 studies of local and global visual processing. It did not find evidence of generally superior local processing or a general deficit in global processing. Instead, the clearest overall finding was that global processing could take longer in autistic participants.

This is important because it means the evidence does not support a simple division in which autistic people process only from the bottom up and non-autistic people process only from the top down.

What does the research actually suggest?

The most defensible conclusion is that some autistic people may show a stronger preference for local or detailed information in certain contexts, while the ability to process the wider picture remains present.

Research findings vary depending on the task, the type of information being processed and the individual participants. Autism is highly varied, so no single processing style applies to every autistic person.

Recent research continues to investigate local and global processing across visual and auditory tasks. For example, a systematic review and meta-analysis of auditory processing found a modest tendency towards local pitch processing in autistic participants, but no overall deficit in global pitch processing.

These findings fit better with the idea of different weighting or preference than with a fixed autistic versus neurotypical processing rule.

Sensory processing differences

Sensory differences are well recognised in autism. Autistic people may be more sensitive, less sensitive or differently responsive to sound, light, touch, smell, taste and other sensory information.

NICE guidance for autistic adults specifically recommends taking hyper-sensory and hypo-sensory sensitivities into account when providing assessment and treatment. The NHS also identifies sensory sensitivity as a common feature of autism.

This means that one autistic person may enter a busy environment and be very aware of fluorescent lighting, several conversations, background music, movement around the room or the texture of clothing. Another autistic person may experience the same environment very differently.

The important point is that sensory experience can vary significantly between individuals.

Attention to detail

Attention to detail is another area that appears repeatedly in autism research.

Some autistic people may notice small changes, inconsistencies or individual features before noticing the broader pattern. In some circumstances this can be useful. In others, it may mean that more time is needed to decide which information is most relevant.

It is better not to describe this automatically as either a strength or a difficulty. Its impact depends on the person and the situation.

Processing time and uncertainty

If somebody is taking in a large amount of sensory or contextual information, they may need more time to understand what is happening and decide how to respond.

This can be particularly relevant in situations that are unfamiliar, socially complicated, ambiguous, noisy or changing quickly.

This does not mean that delayed responding is an inherent feature of autism. However, some autistic people describe needing time to process information before answering a question or making a decision.

Allowing that time can be more helpful than assuming that a slower response reflects confusion, lack of interest or avoidance.

How context can affect understanding

Top-down processing helps people use context to interpret information quickly.

Sarcasm, for example, often depends on tone of voice, facial expression, previous conversation and knowledge of the relationship between the people involved.

Research does not support the idea that autistic people are incapable of understanding context. A more accurate interpretation is that some aspects of global or contextual processing may take longer or be used differently in some situations.

This is more useful clinically than describing autistic people as unable to see the bigger picture.

What can these differences look like in everyday life?

These ideas may help make sense of experiences such as:

• Needing more information before making a decision. Vague instructions such as “just see how it goes” may be difficult because there is not enough information to form a clear plan.
• Noticing changes quickly. Small alterations in a routine, environment or arrangement may be immediately obvious.
• Finding busy environments tiring. A large amount of sensory information may compete for attention.
• Preferring clear communication. Direct information can reduce the need to infer meaning from incomplete or ambiguous social information.
• Needing additional processing time. Someone may understand a situation well but need time to integrate the information before responding.

None of these experiences applies to every autistic person, and none of them alone indicates that somebody is autistic.

What does this mean for therapy?

Understanding information-processing differences can be useful in therapy, particularly when working with autistic clients.

NICE recommends that services take account of predictability, clarity, structure, routine and sensory sensitivities when adapting interventions for autistic adults.

In practice, this can mean:

• using clear and specific language
• explaining what will happen during a session
• avoiding unnecessary ambiguity
• allowing time to answer questions
• providing information in writing where helpful
• considering lighting, sound and other sensory factors
• checking understanding rather than assuming it
• adapting the pace of therapy to the individual

These are not techniques designed to change autistic thinking. They are ways of reducing unnecessary barriers so that therapy is easier to access.

There is no single autistic thinking style

Autism is highly varied. NICE describes autism as a lifelong neurodevelopmental condition whose presentation differs between individuals and can also vary with circumstances and coexisting conditions.

It is therefore misleading to talk about “the autistic brain” as though every autistic person processes information in the same way.

Some people may strongly recognise themselves in descriptions of detail-focused or sensory-led processing. Others may not.

Factors such as ADHD, anxiety, trauma, language, sensory sensitivity, previous experience and the demands of the environment can also affect how somebody processes information.

Bottom-up and top-down processing are useful concepts, but they are better understood as ways of describing aspects of cognition than as explanations for autism itself.

A more useful way to think about processing differences

The value of this research is not in dividing people into two types of brain.

It is in recognising that people can arrive at an understanding of the same situation in different ways.

One person may quickly interpret the overall context and then fill in the details. Another may need to gather more of the details before feeling confident about the overall picture.

Difficulties can arise when an environment assumes that everybody should process information in the same way and at the same speed.

For autistic people, understanding processing differences can sometimes provide a useful explanation for experiences that have previously been interpreted as being overly sensitive, rigid, difficult or slow.

It can also help therapists, employers, families and partners make communication clearer and environments more manageable.

Therapy and neurodivergence

I work with autistic and neurodivergent adults who may be experiencing overwhelm, anxiety, trauma, burnout or difficulties that have developed through trying to function in environments that do not always fit their needs.

Therapy does not need to focus on changing autistic characteristics. Instead, it can involve understanding what is happening, identifying sources of distress and finding ways of working that take account of the person’s individual sensory, emotional and cognitive needs.

You can read more about therapy for ADHD, autism and neurodivergence.

Sources and further reading

• Happé F, Frith U. The weak coherence account: detail-focused cognitive style in autism spectrum disorders. Journal of Autism and Developmental Disorders. 2006.
• Van der Hallen R, Evers K, Brewaeys K, Van den Noortgate W, Wagemans J. Global processing takes time: A meta-analysis on local-global visual processing in ASD. Psychological Bulletin. 2015.
• NICE guideline CG142: Autism spectrum disorder in adults: diagnosis and management.
• NHS: Signs of autism in adults.