The following definition of secondary or higher-order consciousness (also known as "extended consciousness" or "self-awareness") is a fairly typical example from the scientific literature on consciousness:
Higher-order consciousness includes awareness of one's self as an entity that exists separately from other entities; it has an autobiographical dimension, including a memory of past life events; an awareness of facts, such as one's language vocabulary; and a capacity for planning and anticipation of the future" (Rose, 2002, p. 6).
Until recently, secondary consciousness was commonly thought to be unique to human beings and possibly chimpanzees (Rose, 2002, p. 7). One recent development is that the best evidence for most indicators for secondary consciousness now comes from birds (Emery and Clayton, 2004), with the notable exception of self-consciousness.
How are these criteria verified in non-human animals?
Mirror tests are commonly used to show that an animal possesses a concept of self. Gallup, Anderson and Shillito (2002) have successfully defended the mirror test against attempts to discredit its validity. However, some philosophers (Leahy, 1994, pp. 145-146) argue that mirror tests merely indicate that an animal possesses consciousness of its own body, as opposed to true self-consciousness.
As yet, the only evidence that an animal may have an awareness of the 'self' versus awareness of other individuals has been demonstrated in chimpanzees and possibly orang-utans and dolphins (Emery and Clayton, 2004, p. 41).
Reiss and Marino (2001) have reported that dolphins pass the mirror test.
Theory of Mind
Field studies of animals' social interactions (especially signalling and deception) have been used as evidence that they possess a rudimentary theory of mind, but Emery and Clayton (2004) argue that alternative, non-intentional explanations of the behaviour are often possible. It is also unclear how much of the behaviour is unlearned. Emery and Clayton (2004) argue that only controlled laboratory studies on a wide variety of species can establish whether some of them have a theory of mind. At present, the best evidence from controlled laboratory studies for a "theory-of-mind" in animals comes from experimental studies of birds: ravens and western scrub-jays. These birds will delay caching excess food for later use if other individuals are in the vicinity, and wait until would-be thieves are distracted or have moved away before they resume caching. The birds appear to learn this behaviour from their own experience of pilfering other birds' caches (Emery and Clayton, 2004, pp. 17-23). There is tentative evidence for a rudimentary theory of mind in animals as diverse as chimpanzees, dogs and elephants (Horowitz, 2002; Nissani, 2004), but the evidence is not as rigorous compares as the tightly controlled laboratory studies of ravens and scrub jays, described by Emery and Clayton (2004, pp. 15-17). A study by Povinelli (1998) is often cited as evidence that chimpanzees lack a theory of mind, although research by Nissani (2004) seems to overturn some of Povinelli's results.
Language ability in animals is assessed by a variety of procedures, including studies of vocal learning (only six animal groups - humans, cetaceans, bats, parrots, songbirds, and hummingbirds - are capable of this feat (Jarvis et al., 2000)), training animals to use artificial sign language or lexigrams (Budiansky, 1998, summarises work done with chimpanzees and bonobos), interrogation of animals to verify their ability to apply categorial concepts to novel objects, by asking questions such as "What shape?" (Pepperberg, 2002), and controlled studies of allegedly referential alarm calls made by animals to signal the presence of a predator (Cheney and Seyfarth, 1990; Slobodchikoff, 2002; Evans, 2002).
Scientists now know that animals as diverse as parrots (Pepperberg, 2002), dogs (Pilcher, 2004), chimpanzees (Savage-Rumbaugh et al., 1998) and dolphins (Herman, 2002) possess a large receptive vocabulary containing hundreds of words, and are capable of acquiring new concepts relating to colors, shapes and quantities (Pepperberg, 2002), and grasping the meaning of complex vocal and gestural commands (Savage-Rumbaugh et al., 1998; Herman, 2002) as well as novel commands (Herman, 2002) and even commands containing unfamiliar words (Pilcher, 2004). Additionally, there is good evidence of referential communication in birds (Evans, 2002).
Nevertheless, the productive language skills of non-human animals appear to be very limited. The number of signals in their vocal repertoire is small and is restricted to objects experienced in the present, with no evidence of creative production of new sounds for novel situations. Moreover, there is no evidence that animals' vocal calling takes into account what other individuals believe or want (Hauser, Chomsky and Fitch, 2002, p. 1576). Finally, animal calls in the wild seem to have no analogue of names, semantics or syntax (Budiansky, 1998a, pp. 131 - 160; Budiansky, 1998b, pp. 105 - 106).
We may therefore assume that no non-human animal is capable of justifying its actions, in the way required by Kenny (1975) in part B of chapter 4.
This ability is probably unique to human beings. The ability of animals to recall episodes from their past (episodic memory) can be assessed by controlled field studies in which animals are required to recall "when" and "where" information relating to specific items or individuals. At present, the only good evidence for episodic memory in animals comes not from primates but from birds. Western scrub jays can recall information about when a particular food item was cached, as well as what was cached and where (Emery and Clayton, 2004, p. 32). The apparent ability of non-human primates to keep track of who did what to whom and where is currently considered too difficult to test under controlled experimental conditions (Emery and Clayton, 2004, p. 32).
Field observations of great apes are not sufficiently rigorous to establish that future planning is required to account for their behaviour, and most laboratory studies claiming to have tested future planning in animals involve short retention intervals that only relate to the animal's immediate future. Currently the best evidence for future planning in animals is the food-caching behaviour of scrub jays (Emery and Clayton, pp. 35-36).