We have five senses in which we glory and which we recognize and celebrate, senses that constitute the sensible world for us. But there are other senses — secret senses, sixth senses, if you will — equally vital, but unrecognized, and unlauded.

Sacks is challenging the culturally entrenched idea that human experience is neatly bounded by the “five senses.” In his work as a neurologist, he repeatedly encountered forms of perception that are crucial to ordinary life yet rarely celebrated as senses in their own right—proprioception (the sense of bodily position), vestibular balance, interoception (internal bodily states), and the brain’s integrative capacities that make a coherent world from fragmentary inputs. By calling these “secret senses,” he underscores how invisible they are when functioning normally, and how devastating their loss can be. The quote also gestures toward humility: our picture of reality is shaped by the sensory channels we notice and name, not necessarily by the full range of human perceptual life.