Figure 1. The investigation of possible conscious states in non-human species as disparate as birds (a) and cephalopods (b) can be informed by searching for neural properties that have been correlated with consciousness in humans, including reentrant signaling between thalamus and cortex (a, i) or putative functional analogs (b, i), fast, irregular, low-amplitude EEG signals (a and b, ii), and widespread electrical activity in cortex (a, iii) or functionally analogous structures (b, iii).

Such processes in animals can best be related to consciousness when they can be correlated with accurate reports. Relevant forms of report include vocalizations in the case of African grey parrots (a, iv) or coloration and body patterning in the case of cephalopods (b, iv). In the figure, an African grey parrot and a common octopus (O. vulgaris) respond to salient artificial stimuli presented on video displays: an orange block in a discrimination task (a, iv) and a white ball that has been previously associated with food (herring) during training (b, iv) (see Box 1).