Serial order processing for language-based information is critical in everyday activities. When entering a temporary authentication code, it’s not enough to know the right numbers or letters – you have to recall them in the correct order to access your account. This same need for order applies to how we speak, even within speaking a single word. An individual might mean to say “chicken taco” but accidentally say “kitchen taco.” When the sounds for speech are all there but in the wrong order, they can create a mix-up that changes the meaning entirely.
Researchers have found that item identities and their serial order are two separate processes in both working memory and speech production. But one key question remains: is our ability to keep things in order – whether it’s speech sounds in a single word or a list of items in memory – based on the same underlying process?
This question is especially important for people with aphasia, an acquired language disorder that often follows a stroke. Speech difficulties in aphasia can appear different depending on the underlying problem. For instance, saying “dat” instead of “cat” suggests trouble finding the right sounds, while saying “tac” instead of “cat” shows difficulty putting those sounds in the correct order. Many people with aphasia also experience working memory challenges, which can manifest as difficulty remembering what information needs to be maintained and/or in what order it should be recalled.
To explore this, postdoctoral fellow Yingxue Tian, PhD, and institute Faculty Erica Middleton, PhD, and Marja-Liisa Mailend, PhD, investigated the extent to which serial order processing is shared in speech production and working memory. Participants with aphasia completed a word repetition task (repeating a word after hearing it), a word naming task (naming a depicted object), and a working memory task (recalling a list of words). The researchers examined how difficulties in serial order processing in each production task were associated with severity levels of serial order impairment in working memory.
Their study, recently published in Cortex, reveals that the link between serial order processing in speech and working memory depends on the type of production task. When people repeat a word they just heard, their ability to keep the sounds in the correct serial order is linked to how well they maintain serial order information in working memory. But this connection does not hold for the naming task. Instead, serial order processing in naming is associated with the working memory ability to keep track of what items are being remembered, rather than their order.
These findings show that even though both repetition and naming tasks involve saying a word out loud, they draw on different types of working memory. This has important implications for clinical practice, where both tasks are commonly used to assess and treat language difficulties. By understanding how serial order processing works in each task, clinicians can more accurately identify the source of a language impairment and tailor interventions accordingly. Since both speech production and working memory are often affected with aphasia, exploring how they interact can lead to more effective therapies. Targeted interventions that strengthen serial order processing could not only improve word production and working memory but also enhance overall communication and everyday functioning for people living with aphasia.