Automatic and controlled processing of acoustic and phonetic contrasts

Area of Science:

• Auditory Neuroscience
• Speech Perception
• Psychoacoustics

Background:

• Temporal properties of speech signals are vital for phoneme identification and word comprehension.
• Difficulty in detecting temporal speech changes can impair spoken language understanding.
• Finnish language provides examples where vowel duration distinguishes word meaning (e.g., tuli vs. tuuli).

Purpose of the Study:

• To investigate how the position of temporal changes within a word affects speech sound discrimination in native Finnish speakers.
• To evaluate the discrimination of length contrasts in Finnish pseudo-words and their acoustic correlates.
• To correlate brain activity with behavioral measures of speech sound perception.

Main Methods:

• Utilized event-related brain potentials (Mismatch Negativity - MMN, N2b, P3b) to measure cortical responses.
• Incorporated behavioral measures to assess perceptual discrimination of speech sounds.
• Employed three-syllable Finnish pseudo-words with controlled temporal variations at different positions (beginning, middle, end).

Main Results:

• Early auditory processing (indexed by MMN) did not differentiate between speech and non-speech sounds based on temporal changes.
• Differences in processing emerged in later cognitive stages, particularly those involving attention and controlled processes.
• The position of the temporal change within the word influenced speech sound discrimination.

Conclusions:

• Auditory processing of temporal speech features is not solely dependent on early sensory mechanisms.
• Later cognitive processes, influenced by attention and stimulus position, play a significant role in discriminating speech sound variations.
• Findings highlight the complex neural mechanisms underlying speech perception and temporal cue processing.