Nine studies are summarized which investigated the relation between attributes of performance as perceived by the subject and corresponding objective measurements. The attributes studied were: (1) intellectual activity perceived to be involved when dealing with a task (Studies 1 and 2), and (2) perceived difficulty (Studies 4 to 9). Study 3 combined both features. In Study 1, subjects with 9 years of schooling were asked to estimate the degree of qualitative similarity between sample items of 10 tests. Study 2 was basically a replication of Study 1 with high school students in another country. Study 3 investigated the extent to which the perceived difficulty of intelligence tests would covary with the estimates of qualitative similarity. Results on perceived difficulty were summarized in Study 4. In Study 5, involving a simple motor skill task called "wire labyrinth," perceived difficulty was found to be linearly related to performance, with time the only possible objective measurement. Study 6 involved the perceived difficulty of an immediate memory task in which successive messages of 4 to 10 digits were presented acoustically at two digits per second. Ss were to recall them immediately in their original order. Study 7 dealt with the perceived difficulty of a search activity in a visual attention task involving 7 complex stimulus matrices consisting of pairs of consonants. Studies 8 and 9 investigated the perceived difficulty of individual items in 4 tests of intellectual performance. (For related documents, see TM 003 055-061.) (KM)