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Theories of DLD - Coggle Diagram

- - - - Rice and Wexler 1995: no overlap between DLD and HCs in the proprtion of tense markers used
      - Disadvantages
        
        highly specific dysfunctions and cannot account for full range of linguistic or non-linguistic deficits within DLD
        
        Leonard 2000: DLD prevalence is similar across languages; theory would suggest that languages with richer and more complex morphology would have higher prevalence
        
        Bedore and Leonard 2001: cross linguistic differences in DLD presentation (Spanish DLD shows less verb inflection problems
  - - - Rapid Auditory Processing theory: the idea that difficulties with auditory processing rapid information lead to problems with speech perception and then DLD
        
        Deficit most severely impacts processing of acoustically non-salient material (e.g. inflections and function words)
        
        SUPPORT
        
        Tallal and Piercy 1974: children with DLD struggled to discriminate between stop consonants but no difficulty discriminating steady state vowels
        
        Joanisse and Seidenberg 2003: training model with degraded phonological material (to simulate perceptual deficits) lead to grammatical errors similar to DLD
        
        Lyytinen et al 2005: brain responses to auditory stimuli are different in children with DLD vs HCs
        
        DISADVANTAGES
        
        Marshall, Snowling, and Bailey 2004: auditory processing problems are not specific to rapid sequences
        
        van der Lely et al 2004: only has weak associations with DLD
        
        Strong et al 2010: training on temporal processing program does not improve language skills
      - Phonological Working Memory theory: suggests that DLD is caused by a deficit in the ability to store and process verbal material in phonological working memory
        
        this limits the capacity to learn new words and process complex grammar information
        
        GATHERCOE AND BADDELEY 1990: found DLD had shorter working memory spans than HCs but normal effects for word length, acoustic confusability
        
        suggests a severe impairment of phonological memory with no specific difficulties relating to auditory discrimination or articulation speed
        
        study has been replicated with high average effect sizes (avg 1.27- very big)
        
        effect size varied according to
        
        Lexicality: nonwords being similar to real words make it easier
        
        Phonotactics: consonant clusters make it harder
        
        STRENGTHS
        
        WEAKNESSES
        
        root cause is unclear
        
        Vugs et al 2013: theory does not account for visual working memory deficits (although these have a smaller effect size 0.67)
    - - Executive Function theory: suggests deficits in executive functioning can lead to linguistic deficits
        
        moderate impairments on inhibition and cognitive flexibility for DLD group
        
        these group differences were present irrespective of age, modality of task (non/verbal), and severity of language difficulty
        
        could suggest DLD involves broader set of impairments
      - Processing Speed Theories: suggest that children with DLD process linguistic and non-linguistic information more slowly
        
        Lammertink et al 2017: children with DLD show deficits (g= .56) in statistical learning vs HCs with no moderating effects of age or severity of language difficulties
  - - - suggests that because DLD is a heritable condition there should be some genes that cause DLD
      - Reserach suggests that DLD genetics are complex with many genes of small effect
      - Lai et al 2001: FOXP2 (mutation on chromosome 7) is associated with severe forms of DLD and with verbal dyspraxia
        
        this mutation is not associated with more common forms of DLD
        
        this mutation is involved in regulating the expression of other genes which may also be linked to DLD
    - - What is procedural learning
        
        a form of domain-general long term memory store implicated in unconscious/automatic skill-based learning of sequences and patterns, and statistical structures
        
        associated with the frontal area, premotor area, inferior frontal gyrus, and basal ganglia, caudate and putamen
      - Lum, Conti-Ramsden, and Ullman 2013: meta analysis showing an average effect size (.33) of DLD participants performing worse on procedural learning tasks
      - CRITICAL POINTS
        
        group differences were smaller when studies provided more exposure to the sequence (DLD requires more training?)
        
        differences were smaller in older participants
        
        compensatory measures, faster motor responses, etc?
        
        West et al 2017: theory is primarily measured using unreliable behavioural measures
      - Krishnan et al 2022: clear group differences of myelination in the LH cortical language areas, and caudate nucleus