Lawrence E. Marks

The Unity of the Senses

This chapter discusses sensory processes. In these many forms, the unity of the senses reflects fundamental facts of phylogenetic and ontogenetic development. It is commonly believed that all of the senses trace their evolutionary history back to a single primitive sense, a simple undifferentiated responsiveness to external stimulation. It is not difficult to imagine some early form of life, a relatively simple agglutination of cells that wriggled or withdrew when bombarded with virtually any sharp stimulus whether mechanical, radiant, or chemical. The evolution of a visual system out of an undifferentiated sensitivity took one of its most important early steps with the development of special light-sensitive pigments. It has been hypothesized that the senses of hearing and vision, both evolved from an earlier touch sense. That there is currently a close kinship between hearing and the modern touch sense is clear. Both modalities are excited by mechanical energy, that is, by changes in patterns of pressure at the receptors, and both show phenomenological as well as psychophysical similarities.

Interaction among auditory dimensions: Timbre, pitch, and loudness

In two experiments, we examined whether or not pairs of auditory dimensions—timbre-loudness (Experiment 1) and timbre-pitch (Experiment 2)—interact in speeded classification. Subjects classified values from one dimension while the other dimension was (1) held constant (baseline), (2) varied orthogonally (filtering), or (3) correlated linearly. The subjects showed substantial Garner interference when classifying all dimensions—that is, poor performance at filtering relative to baseline. Timbre and loudness displayed redundancy gain (i.e., performance faster than baseline) when correlated positively, but redundancy loss (i.e., interference) when correlated negatively. Timbre and pitch displayed redundancy gain however dimensions were correlated. Both pairs of dimensions showed substantial effects of congruity: Attributes from one dimension were classified faster when paired with “congruent” attributes from the other dimension. The results are interpreted in terms of an interactive multichannel model of auditory processing.

On scales of sensation: Prolegomena to any future psychophysics that will be able to come forth as science

Sensory scales fall into two classes. Type I scales of sensory intensity can be approximated by metric scaling procedures (magnitude estimation, magnitude production) and nonmetric procedures (conjoint measurement); Type I scales are supported by theoretical consideration of sensory processes. Type II scales of sensory dissimilarity can be approximated by metric scaling procedures (category rating, interval estimation, equisection) and nonmetric procedures (analysis of proximities). The psychophysical functions that relate Type I and Type II scales to their corresponding physical scales are in both cases power functions, but the exponents that govern Type I functions are typically about twice as large. Both Type I scales of sensory intensity and Type II scales of sensory dissimilarity are meaningful measures of perceptual experience, but they are measures of different aspects of perception. The duality of sensory scales helps to explain some apparent contradictions among divergent attempts to validate scales of sensation.

Cross-modality matching functions generated by magnitude estimation.

It is possible to generate cross-modality matching functions by having subjects make magnitude estimates of sets of stimuli appropriate to different modalities. The sets are interspersed among each other in the same test session and judged on a common absolute scale of sensory magnitude. An appropriate statistical device locates stimulus levels that appear, on the average, to match. The method is fast, efficient, circumvents the need for continuous stimulus adjustment, and holds promise for the study of the individual as well as the average psychophysical function. To illustrate its potential uses, advantages, and limitations, we used the method to generate cross-modality matching functions relating loudness and brightness. Compared to the scales of loudness and brightness generated by the magnitude estimations of the same stimuli, the matching functions (1) conform better to power functions, (2) may show less variation in slope (exponent), and (3) show far less variation in absolute magnitude (position).

Perceptual primacy of dimensions: support for a model of dimensional interaction

Do Ss always process multidimensional stimuli according to psychologically primary dimensions? Our hypothesis is that they do: Primary dimensions provide one component of a new model of dimensional interaction, a model that distinguishes information processed at the level of attributes from information processed at the level of the stimulus. By using sound stimuli created from the dimensions pitch-loudness (Experiments 1 and 2), pitch-timbre (Experiment 3), and loudness-timbre (Experiment 4), we tested performance in selective- and divided-attention tasks at each of three orientations of axes: 0 degrees, 22.5 degrees, and 45 degrees. Each experiment revealed strong evidence of primacy: As axes rotated from 0 degrees to 45 degrees, selective attention deteriorated, but divided attention improved, producing a distinct pattern of convergence. Each experiment also revealed effects of congruity: Attributes from corresponding poles of a dimension (e.g., high pitch and loud) were classified faster than those from noncorresponding poles. The results fit well with our new conception but are inconsistent with other current models of dimensional interaction.

On Associations of Light and Sound: The Mediation of Brightness, Pitch, and Loudness

Subjects searched for pure tones to match the brightnesses of gray surfaces. Nearly all repeatedly set increasing pitch to increasing brightness; some set increasing loudness to increasing brightness, while others set it to increasing darkness; and most, when brightness was held constant, offset increasing pitch by decreasing loudness. The results mimic those of synesthesia and suggest that most subjects may match auditory to visual brightnesses. The system that mediates these cross-modal equivalences is unknown but may best be thought of as a cognitive mechanism that is capable of manipulating dimensions of sensory experience.

Spatial summation and the dynamics of warmth sensation

Various areal extents of the forehead and back were thermally irradiated at various levels of intensity. For any areal extent, the degree of apparent warmth grows approximately as a power function of intensity level; the larger the area, the smaller the exponent of the power function. Two families of psychophysical functions, one for the forehead, the other for the back, both show that the power functions extrapolate to a point of convergence in the neighborhood of the threshold for pain and tissue impairment. The rules that govern spatial summation of warmth reveal themselvesin the two families. Intensity and area trade one for the other to preserve the same level of warmth. At faint sensation levels, reciprocity is the rule of trading; but with increasing sensation level, area makes a weaker and weaker relative contribution to warmth, and, as a result, it takes a larger and larger percentage change in area to offset a given percentage change in intensity.

Regional sensitivity and spatial summation in the warmth sense

Abstract The magnitude of warmth sensation aroused by heat irradiation and assessed by the method of magnitude estimation depends on the level of the irradiation, its areal extent, and the particular region of the body stimulated. Within a given body region, area and irradiation level both contribute to the magnitude of the warmth sensation (signifying generous spatial summation of neural signals), except that the proportional contribution of area diminishes gradually with increasing level of warmth and finally becomes negligible as the pain threshold is approached. Some regions of the body are far more responsive than others to low-level heating, but all regions respond more or less uniformly when the level of heating is high enough.

On the Cross-Modal Perception of Intensity

Are cross-modality matches based on absolute equivalences between the intensities of perceptual experiences in different senses, or are they based on relative positions within the respective sets of stimuli? To help answer this question, we conducted a series of three experiments; in each the levels of stimulus magnitude in one modality stayed constant while the levels in the other changed from session to session. Results obtained by two methods--magnitude matching and cross-modal difference estimation--agreed in revealing the following: First, the cross-modality matches seem to represent in all cases a compromise between absolute equivalence and relative (contextual) comparison, the compromise being about 50-50 for both auditory loudness versus vibratory loudness and auditory loudness versus visual brightness, but more nearly, though not wholly, absolute for perceived auditory duration versus visual duration. Second, individual variations abounded, with some subjects evidencing totally absolute matching, others totally relative matching (with little consistency, however, between tasks or between comparisons of different pairs of modalities). Third, the judgments of cross-modal difference were consistent with a model of linear subtraction, and in the case of loudness, the underlying scale was roughly compatible with Stevenss sone scale. Finally, a model designed to describe sequential dependencies in response can account for at least part of the context-induced changes in cross-modal equivalence.

Binaural summation of the loudness of pure tones

Subjects made magnitude estimations of the loudness of pure tones (100, 400, and 1000 Hz), which were presented at equal and unequal sound pressure levels to the two ears. The results were consistent with a model of linear binaural loudness summation: The estimates of loudness approximated the linear sum of the loudness estimates of the individual left-ear and right-ear components. The relation between loudness and sound pressure, over moderate SPLs, can be described by a power function with an exponent of about 0.6 at 400 and 1000 Hz, 0.75 at 100 Hz.