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Overview

What Is Intelligence?

The word "intelligence" is associated with actions that are informed, usually by experience or by theoretical knowledge. For instance, an intelligent decision is made by weighing options and ordering priorities, as opposed to acting impulsively. A military commander relies on intelligence gathered in the battle field and by spies in enemy territory. A person with "street smarts" uses practical knowledge and resourcefulness to navigate unfamiliar places. A person with "book smarts" can make inferences based on a bit of data, knowledge of history, and a good theory. Artificial intelligence is trained over many trials, keeping network configurations that "work", so that future tasks can be informed by their history of successes. Other AI comes equipped with "causal models" and other theoretical knowledge.

Why Plants?

Plants are utterly different from animals, and so to take them seriously as candidate "intelligent creatures" poses a challenge to our common sense about intelligence. For the most part, psychology has been led by an introspectivist taxonomy of phenomena. We know of, for instance, emotions that are only known to individuals through socio-linguistic interactions with other people. We have no idea what kind of psychological dark matter lies in wait for a good theory to draw it out, the way relativity theory drew out black holes and gravitational lensing. The plant as subject of psychological inquiry demands new psychology—deeper, more general psychology. By opening up psychology to more than humans and our familiars in the animal kingdom, we will discover new questions, new challenges to standard psychology, and a new world of intelligence to enrich our understanding of mind.

What is so different about plants? Unlike animals, plants don't make their living by eating and metabolizing other creatures (with a few exceptions). Instead, they use water, carbon dioxide, and sunlight to photosynthesize glucose and oxygen for cellular metabolism. The location and availability of these resources, as well as others like dissolved minerals in ground water, change slowly and they can often be cyclical, as with the rise and fall of the sun, or seasonal weather patterns. This means that plants can establish a presence in one place, distributing its resources to the rest of the plant while continuing to forage and expand its presence throughout the habitat. Think of plants as distribution networks, like Amazon and its system of warehouses. It would do no good to move the entire company—headquarters, warehouses, delivery trucks, and the computers from which orders are placed—to every new location its bosses want to set up shop. Plants are everywhere all at once, as compared to animals, who can only go one place at a time. Distribution of roots, shoots, leaves, etc. is highly redundant, so that if one branch runs into trouble, another can take its place. Or if one fails to pan out, there are plenty others in better places. The strategy is an inversion of the old "divide and conquer" offensive strategy: be divided and don't be conquered.

Are Plants Intelligent?

Given the plant's strategy of defense by abundance, we might ask whether any of this requires intelligence. Can plants afford to be dumb, sending out roots and shoots at random, throwing spaghetti against the wall to see what sticks? Consider that animal musculo-nervous systems have many millions more degrees of freedom than they could ever possibly use. Should we assume that animals are dumb too? The evidence for animal and plant intelligence suggests otherwise. Plants possess complicated sensory organs, which influence the distribution of cell elongation, routing and rerouting growth of root and shoot tips. They have elaborate signaling systems, which not only facilitate interactions between distal segments of the plant, but put them in contact with plants, animals, microbes, and fungal networks below the soil. Related, plants make abundant use of volatile substances, metabolites, which make up part of the plant signaling system (as with quorum sensing by bacteria and volume transmission in animal nervous systems). If intelligence is founded on the informing of an organism's activities, then certainly plants count as intelligent. The question remains whether plants can tell us anything new or surprising about intelligence. That is the purpose of our research.

Ecological Plant Psychology

Ecological psychology (EP), founded in the 1960s by James J. Gibson, offers much in the way of conceptual resources regarding the study of plant intelligence. In the matter of intelligence, ecological psychologists argue that even before experience and theoretical knowledge comes into play, the structure of the environment is not only sufficient but necessary for informed action. One example of this is the optical flow field, which is the same for anything sharing the same point of observation, whether plant, animal, or robot. When the point of observation changes, the optical flow field changes systematically, in ways that are specific to changes in the point of observation and changes in the environment. In the example below, moving forward or backward expands or contracts the distribution of optical cones, but their relative position in the flow field remains the same. See this paper for more details and further examples (in the context of plants and plant-inspired robotics).

Animated Gif
Figure 1. A distribution of optical cones extends out from any given point of observation, entirely filling the space (only part of which is available to vision). As the point of observation moves forward or backward, the distribution expands and contracts (respectively). Notice that when one object occludes another, the occluded object's cone disappears.

Thus, in the perspective of ecological psychology, for a creature's activities to be informed, they must be "tuned into" or "resonate with" spatially and temporally varying structure embedded in the ambient energies of its surrounds. These energies include light, air pressure waves, chemical diffusion fields, and any number of other possibilities. Plant roots, for instance, are surrounded by and communicate with a "microbiome" of microbes and fungal networks. And they spread out, with many, highly and multiply sensitive tips. To what extent do any of these bear the kind of spatial and temporal structuring that can serve as information about where to and where not to grow for X, Y, or Z resource? Thus defines the job description for the science of the ecological plant psychologist.

Funding

MINTlab is currently funded by the Office of Naval Research Global (Award No. N62909-19-1-2015) to investigate vegetable sources of bioinspiration for Robotics and AI.


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