 As mentioned in Section 3.3 above, early introspective psychologists both asserted the difficulty of accurately introspecting conscious experience and achieved only mixed success in their attempts to obtain scientifically replicable (and thus presumably accurate) data through the use of trained introspectors. In some domains they achieved considerable success and replicability, such as in the construction of the “color solid” (a representation of the three primary dimensions of variation in color experience: hue, saturation, and lightness or brightness), the mapping of the size of “just noticeable differences” between sensations and the “liminal” threshold below which a stimulus is too faint to be experienced, and the (at least roughly) logarithmic relationship between the intensity of a sensory stimulus and the intensity of the resulting experience (the “Weber-Fechner law”). Contemporary psychophysics—the study of the relation between physical stimuli and the resulting sense experiences or percepts—is rooted in these early introspective studies. However, other sorts of phenomena proved resistant to cross-laboratory introspective consensus—such as the possibility or not of imageless thought (see the entry on  “mental imagery”),  the structure of emotion, and the experiential aspects of of attention. Perhaps these facts about the range of early introspective agreement and apparently intractable disagreement cast light on the range over which careful and well-trained introspection is and is not reliable.