This was an important development, as it attempted to overcome biases that were caused by "language, culture, and education." Further, this scale also provided an opportunity to observe a different type of behavior, because something physical was required. Clinicians were able to observe how a participant reacted to the "longer interval of sustained effort, concentration, and attention" that the performance tasks required. As the Wechsler–Bellevue scale was the first to effectively use the performance scale, it also introduced the "possibility of directly comparing an individual's verbal and nonverbal intelligence". This was possible as "the results of both scales were expressed in comparable units". The Binet scale did have performance tasks, but they were geared toward younger children. The Wechsler-Bellevue was also unique in that there were entire tests that were considered supplements or alternatives, including "performance" measures such as the Leiter International Performance Scale. WAIS The WAIS was initially created as a revision of the Wechsler–Bellevue Intelligence Scale (WBIS), which was a battery of tests published by Wechsler in 1939. The WBIS was composed of subtests that could be found in various other intelligence tests of the time, such as Robert Yerkes' army testing program and the Binet-Simon scale. The WAIS was first released in February 1955 by David Wechsler. Because the Wechsler tests included non-verbal items (known as performance scales) as well as verbal items for all test-takers, and because the 1960 form of Lewis Terman's Stanford–Binet Intelligence Scales was less carefully developed than previous versions, Form I of the WAIS surpassed the Stanford–Binet tests in popularity by the 1960s. WAIS-R The WAIS-R, a revised form of the WAIS, was released in 1981 and consisted of six verbal and five performance subtests. The verbal tests were: Information, Comprehension, Arithmetic, Digit Span, Similarities, and Vocabulary. The Performance subtests were: Picture Arrangement, Picture Completion, Block Design, Object Assembly, and Digit Symbol. A verbal IQ, performance IQ and full scale IQ were obtained. This revised edition did not provide new validity data, but used the data from the original WAIS; however new norms were provided, carefully stratified. WAIS-III The WAIS-III, a subsequent revision of the WAIS and the WAIS-R, was released in 1997. It provided scores for Verbal IQ, Performance IQ, and Full Scale IQ, along with four secondary indices (Verbal Comprehension, Working Memory, Perceptual Organization, and Processing Speed). Verbal IQ (VIQ) Included seven tests and provided two sub-indices; verbal comprehension and