Background: Marissa Ann Mayer (; born May 30, 1975) is an American information technology executive, formerly serving as the president and chief executive officer of Yahoo!, a position she had held starting July 2012. It was announced in January 2017 that she would step down from the company's board upon the sale of Yahoo!'s operating business to Verizon Communications for $4.8 billion. She would not join the newly combined company, now called "Oath," and announced her resignation on June 13, 2017.
Context: Mayer was born in Wausau, Wisconsin, the daughter of Margaret Mayer, an art teacher of Finnish descent, and Michael Mayer, an environmental engineer who worked for water companies. Her grandfather, Clem Mayer, had polio when he was 7 and served as mayor of Jackson, Wisconsin, for 32 years. She has a younger brother. She would later describe herself as having been "painfully shy" as a child and teenager. She "never had fewer than one after-school activity per day," participating in ballet, ice-skating, piano, swimming, debate, and Brownies. During middle school and high school, she took piano and ballet lessons, the latter of which taught her "criticism and discipline, poise, and confidence". At an early age, she showed an interest in math and science.  When she was attending Wausau West High School, Mayer was on the curling team and the precision dance team. She excelled in chemistry, calculus, biology, and physics. She took part in extracurricular activities, becoming president of her high school's Spanish club, treasurer of the Key Club, captain of the debate team, and captain of the pom-pom squad. Her high school debate team won the Wisconsin state championship and the pom-pom squad was the state runner-up. During high school, she worked as a grocery clerk. After graduating from high school in 1993, Mayer was selected by Tommy Thompson, then the Governor of Wisconsin, as one of the state's two delegates to attend the National Youth Science Camp in West Virginia.  Intending to become a pediatric neurosurgeon, Mayer took pre-med classes at Stanford University. She later switched her major from pediatric neuroscience to symbolic systems, a major which combined philosophy, cognitive psychology, linguistics, and computer science. At Stanford, she danced in the university ballet's Nutcracker, was a member of parliamentary debate, volunteered at children's hospitals, and helped bring computer science education to Bermuda's schools. During her junior year, she taught a class in symbolic systems, with Eric S. Roberts as her supervisor. The class was so well received by students that Roberts asked Mayer to teach another class over the summer. Mayer went on to graduate with honors from Stanford with a BS in symbolic systems in 1997 and an MS in computer science in 1999. For both degrees, her specialization was in artificial intelligence. For her undergraduate thesis, she built travel-recommendation software that advised users in natural-sounding human language. In 2009, the Illinois Institute of Technology granted Mayer an honoris causa doctorate degree in recognition of her work in the field of search.  Mayer interned at SRI International in Menlo Park, California, and Ubilab, UBS's research lab based in Zurich, Switzerland. She holds several patents in artificial intelligence and interface design.
Question: What else did she study ?. Whats the answer?
She later switched her major from pediatric neuroscience to symbolic systems, a major which combined