Biomedical subjects

R A Humanski

Publications and source records attributed to R A Humanski.

8 recordsLinked to original sources

PubMed1992

Spatial frequency mechanisms with short-wavelength-sensitive cone inputs.

We have estimated the minimum number and frequency tuning of spatial mechanisms with Short-Wavelength-Sensitive (SWS)-cone inputs. This was accomplished by isolating SWS cones with intense, long-wavelength (yellow) adaptation, and measuring threshold elevation functions for short-wavelength, spatially localized test stimuli masked by obliquely oriented, short-wavelength, cosine gratings. Peak spatial frequency of the cosine gratings and test stimuli varied from 0.25 to 2.83 cpd in 0.5 octave steps. Results derived in this manner demonstrate that SWS cones input to at least two orientation selective mechanisms with peak spatial frequencies of approx. 0.7 and 1.4 cpd, respectively. The frequency tuning of the isolated-SWS-cone, spatial frequency mechanisms resemble closely the lowest two mechanisms measured with luminance modulation (i.e. normal viewing conditions where all cones contribute to the response).

Contrast Sensitivity↗

PubMed1992

Localization of sound in the vertical plane with and without high-frequency spectral cues.

Binaural localization of 3.0-kHz high- and lowpass noise presented in the median vertical plane (MVP) and lateral vertical plane (LVP) was investigated. We anticipated superior performance when localizing the highpass noise by virtue of the availability of pinna cues. The viability of this supposition was strengthened by monaural localization tests in which performance proficiency for the highpass noise exceeded that for the lowpass noise (p less than .01). The main result showed that binaural localization of proficiency for highpass noise surpassed that for lowpass noise for all listening conditions (p less than .01). However, the importance of binaural temporal and level differences in vertical-plane localization was demonstrated by the highly respectable performances when the lowpass noise was presented in the LVP. Data from binaural localization in the MVP and monaural localization in the LVP suggested that the influence of pinna cues diminishes for source elevations above 45 degrees.

Adult↗

PubMed1990

Binaural and monaural localization of sound in two-dimensional space.

Two experiments were conducted. In experiment 1, part 1, binaural and monaural localization of sounds originating in the left hemifield was investigated. 104 loudspeakers were arranged in a 13 x 8 matrix with 15 degrees separating adjacent loudspeakers in each column and in each row. In the horizontal plane (HP), the loudspeakers extended from 0 degrees to 180 degrees; in the vertical plane (VP), they extended from -45 degrees to 60 degrees with respect to the interaural axis. Findings of special interest were: (i) binaural listeners identified the VP coordinate of the sound source more accurately than did monaural listeners, and (ii) monaural listeners identified the VP coordinate of the sound source more accurately than its HP coordinate. In part 2, it was found that foreknowledge of the HP coordinate of the sound source aided monaural listeners in identifying its VP coordinate, but the converse did not hold. In experiment 2, part 1, localization performances were evaluated when the sound originated from consecutive 45 degrees segments of the HP, with the VP segments extending from -22.5 degrees to 22.5 degrees. Part 2 consisted of measuring, on the same subjects, head-related transfer functions by means of a miniature microphone placed at the entrance of their external ear canal. From these data, the 'covert' peaks (defined and illustrated in text) of the sound spectrum were extracted. This spectral cue was advanced to explain why monaural listeners in this study as well as in other studies performed better when locating VP-positioned sounds than when locating HP-positioned sounds. It is not claimed that there is inherent advantage for localizing sound in the VP; rather, monaural localization proficiency, whether in the VP or HP, depends on the availability of covert peaks which, in turn, rests on the spatial arrangement of the sound sources.

Attention↗

PubMed1988

Color perception under chromatic adaptation: red/green equilibria with adapted short-wavelength-sensitive cones.

Chromatic adaptation can dramatically alter the color appearance of a light. The specific effect of adapting short-wavelength-sensitive (SWS) cones is examined by using two adapting wavelengths that lie on a tritanopic confusion line. The change in color appearance caused by signals from adapted SWS cones is isolated by restricting the wavelengths of the test light to 550 nm or longer. Thus the test negligibly stimulates SWS cones, so their sensitivity does not affect the test's appearance. The results show that adapted SWS cones contribute redness to the appearance of a superimposed test light, while not affecting sensitivity of MWS and LWS cones. Quantitatively, the redness from SWS cones illuminated by a large adapting field approaches physical admixture of test and adapting lights. This is very different from an adapting field that stimulates only MWS and LWS cones which, due to a postreceptoral process, contributes much less redness to a small superimposed test than expected from admixture. The difference between the adapted SWS-cone and the adapted MWS/LWS-cone contributions to the color of a small test explains a surprising result: a bluish-green (491 nm) adapting field contributes redness to a superimposed test light.

Adaptation, Ocular↗

PubMed1988

The contribution of the near and far ear toward localization of sound in the sagittal plane.

Eight listeners were required to locate a train of 4.5-kHz high-pass noise bursts emanating from loudspeakers positioned +/- 30, +/- 20, +/- 10, and 0 deg re: interaural axis. The vertical array of loudspeakers was placed at 45, 90, and 135 deg left of midline. The various experimental conditions incorporated binaural and monaural listening with the latter utilizing the ear nearest or ear farthest from the sound source. While performance excelled when listening with only the near ear, the contribution of the far ear was statistically significant when compared to localization performance when both ears were occluded. Based on head related transfer functions for stimuli whose bandwidth was 1.0 kHz, four spectral cues were selected as candidates for influencing location judgments. Two of them associated relative changes in energy across center frequencies (CFs) with vertical source positions. The other two associated an absolute minimum (maximum) energy for specific CFs with a vertical source position. All but one cue when measured for the near ear could account for localization proficiency. On the other hand, when listening with the far ear, maximum energy at a specific CF outperformed the remaining cues in accounting for localization proficiency.

Acoustic Stimulation↗

PubMed1985

Color perception with binocularly fused adapting fields of different wavelengths.

By presenting to one eye a small test superimposed on a background field, and to the other eye only a similar background field of a different wavelength (arranged so that the fused percept is the test centered upon a single fused background), the color appearance of the perceived background can be changed while keeping constant the light stimulating the test eye. Measurements demonstrate that the contralateral field clearly influences the color of the test, even when the left- and right-eye backgrounds are very different in wavelength and illuminance. This change in color appearance cannot be explained (a) by simple contribution of a color signal from the contralateral eye, (b) by the perceived color of the fused background, or (c) by combining the effects of contralateral adaptation (alone) and monocular adaptation (alone). Instead, the central-mechanism response depends on the particular pair of wavelengths that are fused. The results suggest chromatic coding of neural signals arriving at the central locus.

Adaptation, Ocular↗

PubMed1984

Color perception under contralateral and binocularly fused chromatic adaption.

Observers viewed a thin (1.0-1.5 degree) annular mixture of 450 plus 660 nm light with the left eye, and a 4.8 degrees circular 660 nm adapting field with the right eye. The annular test was centered upon the adapting field in the fused percept. The contralateral field, which bleached negligible photopigment, caused the test to appear more reddish; however quantitative results reject the hypothesis that a given contralateral 660 nm light simply adds redness to the test. Additional experiments with a separate 660 nm adapting light presented to each eye reveal that fused chromatic adapting fields affect a complex central mechanism. For example, a dim background presented to the same eye as the annular test can reduce the effect of an opposite-eye field, even when the dim test-eye background has no measurable influence in a purely monocular experiment.

Adaptation, Ocular↗

PubMedDate not supplied

Spatial-frequency adaptation: evidence for a multiple-channel model of short-wavelength-sensitive-cone spatial vision.

The frequency selective effects of spatial adaptation were measured with vertically-oriented, cosine stimuli upon an intense long-wavelength (yellow) field, which isolated the short-wavelength-sensitive (S) cones. Consistent with isolated-S-cone spatial threshold and masking results, the adaptation measurements demonstrate S-cones input to multiple, orientation selective, spatial frequency mechanisms. Moreover, the adaptation measurements show the minimum number of S-cone mechanisms is three. The frequency tuning of each mechanism was derived from the S-cone threshold and masking results. Two of the tuning curves are bandpass with peak sensitivities in a vicinity of 0.7 and 1.4 c/deg, respectively. These two closely resemble tuning curves derived from results with luminance-modulated stimuli. Confined to the range of frequencies examined (0.25-2.83 c/deg), the third tuning curve is lowpass with a high-frequency cutoff of roughly 2.0 c/deg. However, subsequent measurements of orientation selectivity demonstrate the third mechanism to have bandpass frequency tuning as well.

Adaptation, Ocular↗