My colleagues in Finland and I have published another paper on morphological processing in Finnish, a language with a highly complex morphological system. In this paper we look at how morphological and lexical processing differs for healthy older adults and people with Mild Cognitive Impairment or Alzheimer’s disease, compared to healthy younger adults. The paper is available here: https://doi.org/10.1016/j.cortex.2018.
Individuals with Alzheimer’s disease often show declines in semantics (a word’s meaning). It is unclear whether this semantic decline affects morphological processing. In order to answer this question, we tested to what degree word recognition in Finnish was influenced by semantic and form-based (spelling) factors and how the reliance on these factors changes with age and with neuropathology. In line with previous research on Alzheimer’s disease, we found decreased reliance on semantic aspects of word recognition for these patients. However, what was particularly interesting in this study was that healthy older adults and individuals with Mild Cognitive Impairment showed similar patterns to what was found for patients with Alzheimer’s. In other words, all three of the older adult groups showed greater reliance on form-based factors for word recognition than younger adults.
Reading a word activates morphologically related words in the mental lexicon. People with Alzheimer’s disease (AD) or Mild Cognitive Impairment (MCI) often have difficulty retrieving words, though the source of this problem is not well understood. To better understand the word recognition process in aging and in neurodegenerative disorders such as MCI and AD, we investigated the nature of the activation of morphologically related family members in 22 Finnish speakers with AD, 24 with MCI, and 17 cognitively healthy elderly. We presented Finnish monomorphemic (base form) nouns in a single-word lexical decision experiment to measure the speed of word recognition and its relation to morphological and lexical variables. Morphological variables included morphological family size (separate for compounds and derived words) and pseudo-morphological family size (including the set of words that have a partially overlapping form but that do not share an actual morpheme, e.g., pet and carpet, or corn and corner). Pseudo-morphological family size was included to examine the influence of words with orthographic (or phonological) overlap that are not semantically related to the target words. Our analyses revealed that younger and elderly controls and individuals with MCI or AD were influenced by true morphological overlap (overlapping forms that also share meaning), as well as by the word’s pseudo-morphological family. However, elderly controls and individuals with MCI or AD seemed to rely more on form overlap than young adults. This demonstrates that an increased reliance on form-based aspects of language processing in Alzheimer’s disease is not necessarily due to a partial loss of access to semantics, but might be explained in part by a common age-related change of processes in written word recognition.