William James (1842-1910), the eminent American psychologist, was also a licensed medical doctor. He believed that psychology was “ante-science”, meaning that it must ultimately lead to its observations being verifiable by science. The significance of this insight cannot be exaggerated: observational psychology must be accurately and honestly recorded, without bias or personal preference. This is the scientific method. Such is, then, the stated aim of this book’s author (p.2):  “As scientists, however, we must step back from our first-person involvement. We must get a fix on what sensations are objectively about. I’ll return to this over and over again as we go forward.” 

But here is an inherent conflict: if sensations are personal and subjective, its reporting is also personal and subjective, how do you ‘step back from our first-person involvement’? Sadly, what the author has done is not to step back at all, but fully demonstrating, via his stream-of-consciousness writing, what consciousness ‘feels like’, not what it is objectively about.

Sentience: The Invention of Consciousness recounts the author’s early years in Cambridge, England in the 1960s, his involvement in the discovery of blind sight in a monkey and his views of sentience and consciousness today. 

In response to the United Kingdom’s government position, stated in 2021, that recognizes lobsters and other cephalopods as sentient beings, Humphrey in the book concludes (p. 237, note 155): “but what they fail at any point to establish is that lobsters are conscious of pain in the way that humans are, let alone that lobsters possess a phenomenal self that they mind about.” Well, lobsters, like all living things, certainly respond to pain and mind about their own survival! They may not do so exactly as humans do but that doesn’t make them insentient. 

It appears that the words sentience and consciousness need definition.

Sentience and consciousness are related words with slightly different meanings. According to the American Psychological Association:  Sentience. n. 1. the simplest or most primitive form of cognition, consisting of a conscious awareness of stimuli without association or interpretation. 

In this view, sentience is more pervasive than consciousness: "a conscious awareness of stimuli without association or interpretation.” In other words, an animal can be sentient but not conscious: as during anesthesia or from brain damage. This is the opposite of Humphrey’s position: “I suspect sentience may not have arrived until the evolution of warm-blooded animals, mammals and birds, around 200 million years ago.”

And even here, Humphrey does not grant sentience to all mammals, without providing evidence (p. 204): I wouldn’t be surprised if it were to turn out that there are still odd-ball species of mammals and birds that pass none of our tests. It won’t be all mammals and birds that are sentient. Just most of them.

Then frogs, our vertebrate cousins, also do not have sentience—because they don’t do psychology: “If frogs haven’t evolved to be sentient, perhaps it’s because in the world of frogs, there’s no call for doing psychology.”

Well, most humans don’t do psychology as a discipline.

Humphrey’s book here consists largely of random renditions of impressions from a lifetime of contemplation. For example, in his prologue (page x):  soon there will be sentient beings in space. Does he mean finding new kinds of sentient beings in space or that earthlings or their robots have gone there? 

It appears the confusion comes from a lack of consistency in the use of the word consciousness. According to Merriam-Webster, there are multiple levels of meaning of the word consciousness: from awareness inside the self to awareness of the world, to one’s feelings and reactions to the world—and the sharing of these feeling with fellow humans—our shared consciousness. Within the individual, consciousness could be merely the moment of paying attention to what we are looking or thinking about, according to Robert Desimone of MIT, when certain brain neurons fire in unison. This means consciousness is always there, but we are aware of it only when we pay attention. This definition concurs with William James’ 19th Century observation: Consciousness is not a thing, but a process.

But if we look further into consciousness as a condition of living things in general, for example, is the single-celled amoeba conscious?—we run the risk of human judgement. Humphrey here is projecting, without evidence (p.105): “Imagine a primitive Amoeba-like animal floating in the ancient seas. Stuff happens. Light falls on the animal, objects bump into it, chemicals stick to it…The animal, if it’s to survive, must have evolved the ability to sort out the good from the bad and respond appropriately—with a wriggle of acceptance or rejection. When salt arrives at its skin it detects it and ‘wriggles saltily.' When red light falls on it…it ‘wriggles redly.’

Would anyone call this paragraph ‘scientific’? It sounds more like self-indulgence: projecting his own feelings onto the amoeba. Humphrey’s propensity for inventing new words and expressions as convenient is also problematic: how does one ‘wriggle saltily—or redly’?  He also coins the word ‘sentition’ to describe an amoeba’s responses to food or irritant: “Let’s call these reflex responses ‘sentition’, something that hovers between sensation and action. Sentition enacts what the stimulation means to the animal. Indeed, it makes the meaning public.

Nevertheless, Humphrey’s imaginative description of an amoeba’s actions in response to its liquid surroundings may have some scientific merit—that the amoeba could learn from experience and has memory. According to a PubMed article (2009) from the National Institute of Health: “Recently, it was shown that  the amoebalike cell Physarum Polycephalum when exposed to a pattern of periodic environmental changes learns and adapts its behavior in anticipation of the next stimulus to come.” More importantly, this primitive model of learning has been mapped into the response of a simple electronic circuit, potentially leading to discovering how primitive intelligence could have arisen in evolution.

Unfortunately, however, the reader of this book is none the wiser about consciousness—or sentience.