Peter W. Jusczyk, a psychology researcher who showed that infants are able at very young ages to recognize and process sounds related to language, died Aug. 23. Jusczyk, who was 53, was attending a scientific meeting in California. The cause of death was a heart attack.

A funeral mass was held last week in Baltimore.

Jusczyk had been a professor of psychology and of cognitive science in the Krieger School of Arts and Sciences since July 1996. He was an internationally regarded pioneer in the study of infant language perception and speech development and, in 1997, published an influential book on the subject, The Discovery of Spoken Language.

Peter Jusczyk with participants in a 1999 study on infant language perception.

Jusczyk and his wife, Ann Marie Jusczyk, also a Hopkins researcher, operated the Johns Hopkins Infant Language Research Laboratory.

"He was one of the most prolific investigators in our field, and his work was distinguished by important, groundbreaking findings about how infants learn their native language," said Barbara Landau, professor of cognitive science.

Paul Smolensky, also a professor of cognitive science, said, "In an often-contentious field of study, Peter was one of the few persons to be highly respected by researchers from all theoretical perspectives. He provided the kind of leadership role that will be sorely missed."

Greg Ball, a psychology professor and a friend of Jusczyk's, said, "Peter was passionate about everything he did, either in a professional context or for fun." Ball taught a course at Hopkins with Jusczyk called Birds and Words, in which the two professors compared language learning in infants and the learning of bird song, Ball's research specialty.

"I was always impressed by the breadth of his intellect," Ball reminisced. "His thinking was influenced by ideas and findings from many fields, ranging from linguistics to neuroscience or even engineering."

Infants who came to the Johns Hopkins Infant Language Research Laboratory would sit in a booth on the lap of their parent or caregiver and be exposed to taped segments of language and other sounds. Jusczyk tested the infants' ability to understand or process these stimuli by assessing the degree to which they paid attention to them.

For example, Jusczyk and a graduate student studied infants' ability to focus on a particular voice or sound despite distracting background noises, a phenomenon audiologists call the "cocktail party effect." For the 1996 study, researchers first exposed infants repeatedly to a target voice reading a short word, such as "cup" or "dog," while at the same time playing at a slightly lower volume a technical description of a scientific experiment. They would then expose the infants to short taped narratives read by the target voice. Infants would listen longer in the second phase if the narrative contained further use of words that the target voice had read to them in the first half of the experiment.

In another study, Jusczyk found that 4-and-a-half-month-old infants respond to the sound pattern of their names. "It's not that they know 'this is my name' but that the [sound] pattern is familiar to them," Jusczyk said in a 1998 interview with the Baltimore Sun.

In 1999, Jusczyk and colleague Ruth Tincoff presented the first-ever evidence that infants as young as 6 months can associate words with meanings. The words with meanings were the crucial childhood words of "mama" and "dada."

"Most of the previous work on comprehension indicated it was 8 or 10 months of age when kids started to attach labels to particular objects," Jusczyk said at the time. "The difference here is the words name important social figures. This suggests that infants begin forming a lexicon with sound patterns linked directly to socially significant people, such as their parents."

Another aspect of Jusczyk's research focused on determining when infants were able to distinguish between sounds of their native language and other languages based on common sound patterns in their native tongue. He showed that this ability developed sometime between the sixth and the ninth month of infancy.

Jusczyk also frequently studied the ability of infants to recognize the boundaries of words.

"When you hear someone speaking an unfamiliar language, it is hard to tell where one word ends and another begins. How does the pre-linguistic infant cope with this problem?" Jusczyk asked on his Web site.

Jusczyk was born on Jan. 31, 1948, in Providence, R.I. He obtained his bachelor's degree in psychology at Brown University in 1970 and a doctorate in psychology at the University of Pennsylvania in 1975. Before coming to Hopkins in 1996, he held positions at the University of Oregon, the State University of New York at Buffalo, Dalhousie University in Halifax, Nova Scotia, and the Centre Nationale de la Recherche Scientifique, an NIH-like research institution located in Paris.

Among the many professional honors Jusczyk received was his election last year to the prestigious Society of Experimental Psychologists.

Jusczyk's personal interests included bicycling and jazz. He and his wife regularly rode in the Seagull Century, a 100-mile bike ride held every fall on the Eastern Shore of Maryland.

In addition to his wife, Jusczyk's survivors include two children, Karla S. Jusczyk and Thaddeus P. Jusczyk, of Baltimore.

Donations may be sent to the Jusczyk Family Scholarship Fund, c/o Brown University, Box 1893, Providence, RI 02912. The fund is for student-athletes at Brown who pursue higher degrees in the sciences.