Rosch et al. (1976), properties of items within the environment are not independent, but rather certain attributes tend to co-occur within specific categories. However, this is not a requirement for ad hoc category membership, given that relatedness is construed based on goal satisfaction rather than featural relatedness. Second, in contrast to taxonomic categories, ad hoc categories are often constructed on-line, and thus are not well established within long-term memory. However, it is thought that while ad hoc categories are representationally distinct from taxonomic categories, they exhibit a comparable graded similarity structure, in which a member of the category may be seen as more prototypical of the given category compared to other members. Barsalou (1991) used the classic ad hoc category example of things to pack for a vacation. When packing for a trip, one actively constructs this category in order to pack the appropriate items. For new goal-based categories, planners must derive the ad hoc categories themselves before they can consider and select appropriate category members, or instantiations. Planners would then use well established knowledge of other categories to generate candidates for the ad hoc category and then test them for membership. For example, one might use the established knowledge of the category of clothing to consider whether or not they need to pack a bathing suit for their vacation- if they decide in the affirmative, then bathing suit becomes a member of the ad hoc category. Thus, Barsalou (1991) posited that ad hoc category members would not necessarily share many features (i.e., bathing suit, money, toothpaste), but would nevertheless be members of the same ad hoc category because they similarly satisfy the requirements of the current behavioral goal of things to pack for vacation. This work has been exceptionally influential within the study of categories, and has played a large role in illuminating the flexibility of semantic relatedness and the influence of specific behavioral goals on short and long-term conceptual representations. Grounded cognition Barsalou has also been an outspoken advocate for grounded views of cognition, and has developed several influential models of grounded cognitive processing within specific domains. According to traditional cognitive theory, semantic memory is represented in an amodal format and is distinct from the low-level perceptual processes used to encode information from the surrounding environment. However, beginning with the influential work by Lakoff & Johnson (1980), some cognitive scientists, including Barsalou, have posited that cognitive representations are