Lisa D. Sanders - US grants

I plan to explore the ways in which different types of auditory information, including linguistic, biological, and artificial sounds, are processed in the brain. More specifically, I will measure normal adults' abilities to discriminate these stimuli based on both motion and brief temporal differences. It is possible that linguistics stimuli, for which fast temporal processing is crucial, may be more easily processed in terms of motion. By matching non-identifiable sounds in complexity, spectral change, and band-width to each of the types of stimuli mentioned above, it will also be possible to determine if differences in the ways in which these sounds are processed are best attributed to physical differences in the stimuli or to the goals of processing. If the different types of stimuli are processed differently, it is likely that such processing involves different cortical areas. By using ERP and MEG methods, it will be possible to determine the precise times at which the processing of these different stimulus types is differentiated into different cortical pathways. By using fMRI, it will possible to determine which cortical areas are involved in processing auditory stimuli are involved in processing auditory stimuli with specific physical features and for specific goals.

DESCRIPTION (provided by applicant): Selective attention plays an important role in perception under a wide variety of conditions in which people are presented with too much information. Spatially selective attention allows observers to preferentially process a few of many simultaneously presented images or sounds. However, less is known about the role of temporally selective attention in allowing people to preferentially process information presented at specific times. The goals of this project are to describe the parameters of selective auditory attention directed to time periods, to explore the neural mechanisms involved in temporally selective attention, and to determine if temporally selective attention plays a role in efficient speech perception. In a series of five experiments, listeners will be directed to attend to specific times by individual symbolic cues, rhythms, and natural speech. Auditory temporally selective attention will be indexed by comparing event-related potentials (ERPS) elicited by physically identical non-target sounds presented at attended and unattended times. Just as studies of spatially selective attention have contributed to an understand of how people process large amounts of visual information presented simultaneously, the proposed studies can contribute to an understanding of how people process large amounts of rapidly presented auditory information. Continuous speech, one example of rapidly changing acoustic information, may require temporally selective attention for efficient processing. The proposed research will provide evidence about differential processing of sounds presented at attended and unattended times as well as how listeners select information for preferential processing. Therefore, it will contribute information of practical significance to the design and implementation of training programs for individuals in perceptually challenging environments, acquiring new skills, and with rapid processing deficits. Since temporal attention may be particularly important for speech perception, the results have important implications for improving communication skills in language-impaired children, adults with aging-related hearing lose, and individuals adjusting to perception through cochlear implants.

Understanding how humans comprehend speech is an unsolved and challenging problem, in part because factors such as different speakers, dialects, and speaking rates introduce a great deal of temporal and spectral variability into the speech signal. The focus of this research is on the influence of temporal context on perception of segments, syllables, and words. Results of the research may offer insights into treatment of disorders that involve disruption of speech rate (e.g., dysarthria, stuttering, Parkinson's disease, and aphasia), inform approaches to improve speech technology applications (e.g., enhanced automatic speech recognition, more natural sounding computer-generated speech), and lead to new discoveries related to brain mechanisms involved in understanding spoken language. The investigators will also involve students in the research, including those from a primarily undergraduate institution collaborating on the project.

The investigators will test different accounts of temporal phenomena in the perception of speech. They propose two interacting cognitive mechanisms controlling phenomena at lexical and phonetic levels, each driven by a different neural timing mechanism. The hypothesis is that effects of lexical rate primarily stem from top-down, speech-specific temporal expectancies, while phonetic rate effects originate in bottom-up, transient rhythmic expectations that are not specific to speech. This hypothesis will be assessed using psychoacoustic studies, non-invasive measures of brain activity, and theoretical modeling in order to identify the processing characteristics revealed by neural representations of temporal properties of speech.

One of the core issues in linguistics is how language is acquired. Do people learn a language the way a bird learns its song, using special-purpose brain mechanisms? Or do they learn it the way they learn chess, using general-purpose intelligence? The answer to this question is crucial for understanding how people learn a first or second language, how language learning is connected to other kinds of learning, how the brain stores its knowledge of language, and how humans evolved the capacity for language. The answer might even be different for different aspects of language, such as sounds vs. vocabulary vs. sentence structure. It is especially important for understanding why language is not always learned successfully, either by children acquiring their first language, or adults learning a second language. At a broad level, understanding how to improve language learning has positive impacts for a society--improved cultural diplomacy, economic growth, increased communication in an immigrant nation--and for individuals--personal fulfillment and cognitive benefits associated with language study.

Studies of general-purpose intelligence have identified two separate learning systems which approximately correspond to "reasoning" and "intuition". They are activated by different kinds of learning situation, cause different electrical activity in the brain, and are good at learning patterns with different structures. It is not known how these two systems are involved in language acquisition. This project asks how reasoning and intuition are involved in the second-language acquisition of the "sound pattern of a language--that is, how sounds combine to form larger units like syllables and words. The project also asks whether certain patterns are easier to learn either due to their structure or content. The researchers will teach people invented languages whose properties can be manipulated, and measure both learning performance and the brain's electrical response to ask whether the language learners show the characteristic signatures of reasoning and intuition found in learning non-linguistic patterns, or whether different mechanisms are being used. The results will illuminate factors that affect the success of language learning. To foster robust and reliable science in the area of language learning, the investigators will disseminate, for each of the project's experiments, "replication kits" that will include all stimulus files, instructions for setting up the experiments on the user's computer, and software scripts for running the experiments and for data analysis.

Reading is an essential skill in modern society. Developing effective methods for teaching reading, and effective interventions for reading difficulties and disabilities, requires an understanding of the cognitive processes involved in fluent reading. Recent research has suggested that skilled reading may be aided by our ability to predict upcoming words. Readers use their knowledge of their language and the world to anticipate or predict the words that they are likely to encounter; words that are correctly predicted are more easily recognized. The present research investigates this phenomenon in detail, comparing data from two state-of-the-art methods: 1) tracking of readers' eye movements and 2) recording of Event-Related Potentials (ERPs), which reflect the brain's activity in response to individual words. Both methods show reliable changes in response to a word's predictability. A paradox that motivates the present research is that eye movements reflect a word's predictability only when the word can be pre-processed in peripheral vision, before it is directly inspected. In contrast, ERPs reflect a word's predictability even without such pre-processing. By achieving a better understanding of what these two methods are telling us, and the source of the differential effects, the investigators hope to further our knowledge of the ways in which making unconscious predictions about upcoming words can benefit readers.

The researchers test the hypothesis that predictability influences eye movements through an influence on early orthographic processing, which is carried out in parafoveal vision while a word is not viewed with maximum visual acuity. This implies a Bayesian account of the predictability effect, whereby the influence of a contextually based prior is strong only when perceptual evidence is relatively ambiguous. The effect of predictability in ERPs is thought to be an entirely distinct effect on late, integrative processes. To test the predictions of these hypotheses, eight eye-movement experiments using the boundary paradigm (in which a word is replaced by a different word until it is directly fixated) will be carried out. Three of these experiments also require participants to detect the change from preview to target explicitly, as the hypotheses make novel predictions about the circumstances in which such changes are detectable. Two of the experiments combine eye-movement recording and the boundary paradigm with concurrent ERP measures. In these experiments the effects of predictability on eye movements and ERPs are expected to be fully dissociable, with one or the other emerging depending on the nature of the preview word and the target word. Finally, the E-Z Reader model of eye movements in reading will be modified to account for these effects, as well as other predictability-related phenomena. A new, publicly available implementation of E-Z Reader will be developed, which will allow other researchers to evaluate the model's architecture and test the effects of changes to model parameters.