The octopus is an invertebrate whose brainpower has fascinated scientists, possessing problem-solving abilities that rival many vertebrates. Their complex behaviors raise questions about the nature of consciousness and self-awareness in creatures so distantly related to humans. The question of whether an animal recognizes its own reflection is a method for probing this self-awareness, leading researchers to apply the classic mirror test to these intelligent mollusks. Understanding the octopus’s reaction to its own image can provide insights into how self-perception might evolve in a completely different nervous system structure.
What Defines Self-Recognition
The mirror test, formally termed the mark test or self-recognition (SMR) test, is the standard procedure used to assess an animal’s capacity for self-recognition. Developed by psychologist Gordon Gallup Jr. in 1970, the test aims to determine if an animal understands that the reflection it sees is its own body and not another individual. The methodology involves covertly placing an odorless, colorless mark on a part of the animal’s body that it cannot typically see without a mirror. An animal passes the test if, upon seeing its reflection, it consistently directs behavior toward the mark, such as touching or investigating it.
This self-directed behavior suggests the animal possesses a cognitive model of its own body and recognizes the mark as an unusual feature on itself, indicating a level of self-awareness. Only a limited number of species have passed this assessment, including great apes, bottlenose dolphins, elephants, and Eurasian magpies. The successful passage of the test by these species establishes a baseline for comparing the cognitive abilities of other animals, like the octopus, in the context of self-perception. However, critics acknowledge that failing the test does not necessarily preclude self-awareness, especially in species that rely more heavily on non-visual senses.
The Remarkable Cognitive Abilities of Octopuses
Octopuses are considered the most intelligent invertebrates, exhibiting complex behaviors that suggest advanced cognition. Their nervous system is highly decentralized, with approximately two-thirds of their neurons located in the nerve cords of their eight arms, allowing the arms to process information independently of the central brain. This unique neural architecture contributes to their problem-solving skills, which include unscrewing jar lids to access food and escaping from secure enclosures.
Certain octopus species are among the few invertebrates known to use tools, such as the veined octopus (Amphioctopus marginatus) carrying coconut shells for protective shelters. They display a sophisticated ability to instantaneously alter their skin texture and color for camouflage, sometimes mimicking other marine animals. They can also learn by observing the behavior of other octopuses. These behaviors, alongside their capacity for long-term memory and object manipulation, position the octopus as an exceptional candidate for studies exploring non-vertebrate intelligence.
Applying the Mirror Test to Octopuses
Given their cognitive prowess, researchers have applied the mark test to octopuses, most notably with the common octopus (Octopus vulgaris). In studies exposing octopuses to mirrors, the initial reaction is often a shift in behavior, such as increased exploratory responses toward the reflective surface. Some octopuses perform agonistic displays, such as the “passing cloud” skin pattern, directed at the mirror, suggesting they initially perceive the reflection as a conspecific or rival.
However, when the full mark test procedure is implemented, octopuses generally do not exhibit the self-directed behavior necessary to constitute a pass. In one preliminary study, Octopus vulgaris were marked with non-toxic nail polish. Their frequent mark-directed exploration was also observed in the absence of a mirror or in sham-marked individuals, suggesting the behavior was driven by tactile or proprioceptive stimuli from the mark itself. Thus, they have not yet demonstrated visual mirror self-recognition, despite showing curiosity and complex reactions to their reflections.
Alternative Measures of Octopus Self-Awareness
The failure of octopuses to pass the visual SMR test does not mean they lack self-awareness, as the test may be ecologically inappropriate for their unique biology. Octopuses primarily rely on chemosensory and tactile information; their arms are highly sensitive to chemical cues and touch, which may override the importance of a visual mark. Their laterally placed eyes and lack of color vision mean their visual perception is fundamentally different from that of the visually-dominant vertebrates for whom the test was designed.
Researchers are exploring alternative behaviors that suggest a concept of self and high-level cognition. Octopuses exhibit object play, manipulating items with their water jet or arms, which may be a form of motor exploration linked to reducing uncertainty. They also display a negative response to uncertainty, motivating them to explore and learn about their surroundings. The ability of an octopus to monitor and protect a damaged area, and to learn to associate locations with pain relief, suggests an awareness of their own physical state, a component of self-awareness that is not strictly visual.