The term 'signal' occupies a surprisingly wide conceptual territory across the depth-psychology corpus, appearing not as a unified construct but as a contested boundary object between ethology, neuroscience, semiotics, and psychodynamic theory. In ethological framing—most fully developed by Lench via Maynard Smith and Lorenz—a signal is distinguished from a cue by its intentional communicative function: signals coevolve between sender and receiver, serving mutual adaptive interests, whereas cues convey information incidentally. This distinction carries direct consequence for understanding emotional expression, particularly grief, weeping, and submission displays, as biologically prepared, stereotypic transactions rather than mere epiphenomena. Simondon extends the concept into an information-theoretic register, treating the signal as that which is essentially unpredictable—the bearer of decision-capacity—whose signification emerges only through 'disparation' between an incoming signal and a receiver's pre-existing form. Kandel and neurobiological writers invoke signal in the classical electrophysiological sense: action potentials, calcium-mediated neurotransmitter release, and neuromodulatory teaching signals (dopamine reward-prediction error in Schultz). Lacan appropriates the Freudian signal-anxiety formulation, reading the ego's withdrawal of cathexis as the mechanism producing anxiety as a warning signal. Flores situates shame as a psychosocial signal marking boundary violations. Together these voices reveal a central tension: whether signal is primarily a biological transmission mechanism, an evolutionary communicative act, or a semiotic-structural event requiring a receiving context to produce meaning.
A signal is a functional communicative act... signals initiate a transaction that is commonly beneficial to both the signaling and observing animals.
Lench establishes the signal/cue distinction from ethology as foundational for understanding emotional expression, defining signals by their functional, co-evolutionary communicative intentionality rather than incidental information transfer.
, The Function of Emotions: When and Why Emotions Help Us, 2018thesis
Unlike cues, in the case of signals, both the signaling behavior and the response of the observer are stereotypic: they coevolve.
Lench argues that the defining feature of a signal is the co-evolved stereotypy of both emission and reception, distinguishing it fundamentally from unilaterally decoded cues.
, The Function of Emotions: When and Why Emotions Help Us, 2018thesis
The information signal is therefore the capacity to decide, and the 'quantity of information' that can be transmitted... is proportionate to the number of significative decisions that this system can transmit or register.
Simondon defines the information signal as intrinsically unpredictable—the carrier of decision rather than mere repetition—making unpredictability the structural criterion of genuine signification.
, Individuation in Light of Notions of Form and Information, 2020thesis
For a signal to receive a signification not only in a psychological context but also in an exchange of signals between technical objects, there must be a disparation between a form already contained in the receiver and an information signal provided from the outside.
Simondon argues that signification requires structural mismatch—disparation—between receiver and signal, so that meaning emerges from irreducible difference rather than correspondence.
, Individuation in Light of Notions of Form and Information, 2020thesis
The ego withdraws its (preconscious) cathexis from the instinctual representative that is to be repressed and uses that cathexis for the purpose of releasing unpleasure (anxiety).
Lacan, reading Freud's signal-anxiety theory, frames the ego's mobilization of anxiety as a purposive deployment of redirected libidinal energy serving as a warning signal against repressed drive-representatives.
, The Seminar of Jacques Lacan, Book VIII: Transference, 2015thesis
Consistent with an ethological signal, expressions of grief have a marked impact on the thoughts, feelings, and actions of those who witness them.
Lench applies the ethological signal framework to grief, arguing that weeping functions as an evolved communicative act that reliably elicits stereotypic prosocial responses in observers.
, The Function of Emotions: When and Why Emotions Help Us, 2018supporting
Since signals are intended to be communicative, signals evolve toward conspicuousness and redundancy.
Lench traces how the evolutionary pressure toward effective communication drives signals to become multimodal and exaggerated, explaining the conspicuous visual and auditory features of weeping.
, The Function of Emotions: When and Why Emotions Help Us, 2018supporting
The dopamine error signal could be a teaching signal that affects neuronal plasticity in brain structures that are involved in reward learning, including the striatum, frontal cortex, and amygdala.
Schultz identifies the dopamine prediction-error response as a teaching signal whose function is to update synaptic plasticity, grounding reward learning in a neurochemical signal mechanism.
, Dopamine reward prediction error coding, 2016supporting
Voltage-gated calcium channels opened by the action potential start the process of translating an electrical signal into a chemical signal, just as in the receiving cell, transmitter-gated channels translate chemical signals back into electrical signals.
Kandel describes the reciprocal transduction between electrical and chemical signals at the synapse, establishing the neurobiological signal as a bidirectional translation process fundamental to neural communication.
, In search of memory the emergence of a new science of mind, 2006supporting
In implicit memory storage, the attentional signal is recruited involuntarily (reflexively), from the bottom up... In spatial memory, dopamine appears to be recruited voluntarily, from the top down.
Kandel distinguishes bottom-up from top-down attentional signals as parallel but architecturally different modulatory mechanisms that converge on shared molecular machinery for memory consolidation.
, In search of memory the emergence of a new science of mind, 2006supporting
The repeated learning trials required for sensitization are important because they send signals to the nucleus, telling it to activate regulatory genes that encode regulatory proteins.
Kandel proposes that repetition in learning functions as a nuclear signaling cascade, linking behavioral training to gene expression and thereby to the structural consolidation of long-term memory.
, In search of memory the emergence of a new science of mind, 2006supporting
Signal for violations
Flores positions shame as a psychosocial signal specifically indexed to boundary violations, assigning it a regulatory function within a healthy narcissism-shame balance.
, Group Psychotherapy with Addicted Populations An, 1997supporting
There have been many proposals concerning the major signals that may mediate the homeostatic control of feeding, including glucostatic, aminostatic, lipostatic, and thermostatic theories of regulation.
Panksepp surveys competing hypotheses about the peripheral signals governing feeding homeostasis, framing hunger regulation as a competition among candidate signal modalities converging on hypothalamic control.
, Affective Neuroscience The Foundations of Human and Animal, 1998supporting
As methods of recording electrical signals continued to improve, a small electrical signal was discovered at the synapse between motor neurons and skeletal muscle.
Kandel recounts the empirical discovery of the synaptic potential as an electrical signal that resolved the debate between chemical and electrical transmission theories of neural communication.
, In search of memory the emergence of a new science of mind, 2006supporting
Vervet monkeys in East Africa give different alarm cries depending on whether an observed predator is a leopard, eagle, or snake. Other vervets then respond appropriately whether or not they have seen the predator.
James's text illustrates the signal concept through primate alarm call differentiation, demonstrating that discrete signals can encode referential information and elicit species-specific adaptive responses.
, The Principles of Psychology, 1890aside