Role of slow temporal modulations in speech identification for cochlear implant users.

OBJECTIVE: This study aimed to assess whether the capacity of cochlear implant (CI) users to identify speech is determined by their capacity to perceive slow (< 20 Hz) temporal modulations. DESIGN: This was achieved by studying the correlation between (1) phoneme identification in quiet and in a steady-state or fluctuating (8 Hz) noises, and (2) amplitude-modulation detection thresholds (MDTs) at 8 Hz (i.e. slow temporal modulations). STUDY SAMPLE: Twenty-one CI users, unilaterally implanted with the same device, were tested in free field with their everyday clinical processor. RESULTS: Extensive variability across subjects was observed for both phoneme identification and MDTs. Vowel and consonant identification scores in quiet were significantly correlated with MDTs at 8 Hz (r = - 0.47 for consonants, r = - 0.44 for vowels; p < 0.05). When the masker was a steady-state noise, only consonant identification scores tended to correlate with MDTs at 8 Hz (r = - 0.4; p = 0.07). When the masker was a fluctuating noise, consonant and vowel identification scores were not significantly correlated with MDTs at 8 Hz. CONCLUSIONS: Sensitivity to slow amplitude modulations is correlated with vowel and consonant perception in CI users. However, reduced sensitivity to slow modulations does not entirely explain the limited capacity of CI recipients to understand speech in noise.

Memory for Random Time Patterns in Audition, Touch, and Vision.

Perception deals with temporal sequences of events, like series of phonemes for audition, dynamic changes in pressure for touch textures, or moving objects for vision. Memory processes are thus needed to make sense of the temporal patterning of sensory information. Recently, we have shown that auditory temporal patterns could be learned rapidly and incidentally with repeated exposure [Kang et al., 2017]. Here, we tested whether rapid incidental learning of temporal patterns was specific to audition, or if it was a more general property of sensory systems. We used a same behavioral task in three modalities: audition, touch, and vision, for stimuli having identical temporal statistics. Participants were presented with sequences of acoustic pulses for audition, motion pulses to the fingertips for touch, or light pulses for vision. Pulses were randomly and irregularly spaced, with all inter-pulse intervals in the sub-second range and all constrained to be longer than the temporal acuity in any modality. This led to pulse sequences with an average inter-pulse interval of 166 ms, a minimum inter-pulse interval of 60 ms, and a total duration of 1.2 s. Results showed that, if a random temporal pattern re-occurred at random times during an experimental block, it was rapidly learned, whatever the sensory modality. Moreover, patterns first learned in the auditory modality displayed transfer of learning to either touch or vision. This suggests that sensory systems may be exquisitely tuned to incidentally learn re-occurring temporal patterns, with possible cross-talk between the senses.

A perceptual-economy account for the inverted-optimal viewing position effect.

In reading, fixation durations are longer when the eyes fall near the center of words than when fixation occurs toward the words' ends-the inverted-optimal viewing position (I-OVP) effect. This study assessed whether the I-OVP effect was based on the fixation position in the word or the fixation position in the visual stimulus. In Experiments 1-3, words were presented at variable locations within longer strings of symbols. On trials with short fixation durations, there were effects of fixation position in the string. When long fixations were made, there were effects of fixation position in the word. In Experiment 4, an I-OVP effect was found for meaningless number strings, and its strength depended on the task's processing demands. The findings show that (a) the I-OVP effect is unrelated to orthographic informativeness and (b) the eyes are not constrained to spend more time at the center of visual stimuli. These results support a perceptual-economy account: Fixations are held longer when the eyes are estimated to be at locations in words/stimuli in which greater amounts of information are anticipated. Implications for eye movements in reading are discussed.

Influence of foveal distractors on saccadic eye movements: a dead zone for the global effect.

Three experiments investigated the global effect with foveal distractors displayed in the same hemifield as more eccentric saccade targets. Distractors were x-letter strings of variable length and targets corresponded to the central letter of letter strings (e.g., 'xxxkxxx'). Results showed that only foveal distractors longer than four letters (about 1 degree) deviated the eyes in a center-of-gravity manner thus suggesting a dead zone for the global effect. Short distractors influenced the likelihood of small-amplitude saccades (less than about 1 degree) and the latency of longer saccades. The findings were interpreted based on the dissociation between fixation and saccadic neurons. Implications for eye movements in reading were discussed.

Eye movements in reading isolated words: evidence for strong biases towards the center of the screen.

Three experiments were conducted that compared the eye movement pattern to a peripheral word or letter string as a function of the position of an initial fixation stimulus relative to the center of the screen and the straight-ahead position. Results revealed a strong bias of the eye behavior towards the center of the screen, but not towards the straight-ahead position. Saccades were greater in length, and landed closer to the center of words/strings when launched from a position left of center than when launched from either center or right part of the screen. In addition, the initial saccade launch site was deviated to the right, or to the left of the initial fixation stimulus depending on where relative to the center of the screen the fixation stimulus was displayed. Data were interpreted with the assumption that saccades are programmed in a visual reference framework, with saccade amplitude being computed in relative coordinates. Further research will determine whether the observed bias generalizes to text reading.