Lexical processing depends on sublexical processing: Evidence from the visual world paradigm and aphasia

Area of Science:

• Neuroscience
• Psycholinguistics
• Speech Perception

Background:

• Previous research on aphasia yielded conflicting results regarding lexical versus sublexical speech perception.
• Some studies suggested direct mapping from acoustic information to lexical representations, challenging the necessity of sublexical processing.

Purpose of the Study:

• To investigate the dependence of lexical speech processing on sublexical processing in individuals with aphasia.
• To provide converging evidence using synthetic speech and eye-tracking methodology.

Main Methods:

• Eight individuals with aphasia and ten controls completed visual world paradigm tasks for phoneme (sublexical) and word (lexical) identification.
• Synthetic speech stimuli varied on a voice-onset time continuum were used.
• Eye-tracking monitored online speech perception processes.

Main Results:

• Strong correlations were found between sublexical and lexical task performance in both identification and eye-movement data.
• No patient with normal lexical task performance showed impairment on the sublexical task.
• Results support a hierarchical model where sublexical processing underpins lexical processing.

Conclusions:

• Lexical speech processing is dependent on intact sublexical processing abilities.
• Findings have implications for understanding aphasia and assessing speech processing deficits.