Spatial Frequencies and Hemispheric Processing Dave Peterzell - PDF document

Spatial Frequencies and Hemispheric Processing Dave Peterzell Spatial Frequencies 1

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High Contrast Sensitivity Low Low High Spatial-Frequency 5

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From Delis, Robertson & Efron, 1986 Dichotomania • Mind Left vs Mind Right • “The Decline & Fall of Hemispheric Specialization” (Efron, 1990) 7

Justine Sergent • McGill University and Montreal Neurological Institute • Visiting scholar at CalTech w/ Sperry • d. 1994 • Cognitive neuroscientist, some knowledge of vision • Wordered about the interaction between sensory variables, cognitive performance, and hemispheric asymmetry. • Task X stimulus X VF/Hemisphere Justine Sergent • McGill University and Montreal Neurological Institute • Visiting scholar at CalTech w/ Sperry • d. 1994 • Cognitive neuroscientist, some knowledge of vision • Wordered about the interaction between sensory variables, cognitive performance, and hemispheric asymmetry. • Task X stimulus X VF/Hemisphere 8

Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? • “The frequency contents of small letters 3x higher than large.” • Targets: L, H • Non-targets: T, F • “This study will consider as a main variable…” p 257. Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? “Yes” if L,H present in large or Small or both letters. “No” if L, H present in stimulus 9

Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? Shorter duration, Mask to prevent encoding high SFs (so only large stimuli are detectable) LVF/RH advantage Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? "...The modes of hemispheric processing (may) differ by the components of the sensory inputs to which each hemisphere is preferentially sensitive: The right hemisphere (RH) displays greater efficiency than the left hemisphere (LH) at processing early-available low- spatial-frequency contents of a visual image; the LH is better equipped than the RH to deal with later-available high frequencies of a stimulus. This implies that both hemispheres can deal with verbal and nonverbal stimuli but do not operate on the same components of the sensory outputs. It is thus argued that hemispheric asymmetries emerge (a) only when cognitive operations are performed and (b) as a function of the stimulus frequency components required to acheive the task and available given the viewing conditions and/or the spatial organization of the stimulus" (p. 253). 10

Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? "This view points to a model of cerebral lateralization allowing for the bilateral representation of information, but recognizing differential adaptation of each hemisphere to operate on the neural representation of that information" (p. 267).” Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? "This view points to a model of cerebral lateralization allowing for the bilateral representation of information, but recognizing differential adaptation of each hemisphere to operate on the neural representation of that information" (p. 267).” "It would then appear that the characteristics of the neural representations on which cognitive operations are performed may constitute the basis on which cerebral lateralization is built. This is not to deny the existence of the more traditional dichotomies, but rather to argue that such dichotomies result from--and are explained by--a more fundamental dissociation" (p. 267) 11

Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? "Although this hypothesis is essentially based on data in the visual modality, it is obviously meant to apply to other modalities. In the auditory domain,... there is evidence that high temporal resolution information (verbal or nonverbal) is more rapidly and accurately processed when presented to the right than to the left ear, and the opposite outcome is found with low resolution information (Thatcher, 1980). The result is obtained despite the equal capacities of the left and right sensory auditory areas to decect formants of all bandwidth (Molfese, 1978), suggesting that the asymmetry emerges beyond the sensory level. Similarly, discrimination of duration is better achieved in the LH than the RH, but only when the intervals are of 50 msec or less (Mills & Rollman, 1979), indicating a greater temporal resolution capacity in the LH" (p. 267). Sergent (1982). The Cerebral Balance of Power: Confrontation or Cooperation? "This discussion suggests that the same cognitive operation may require the involvement of both hemispheres, with the RH more adept at preliminary and low-resolution processing and the LH at later and high-resolution processing. This points to a cooperation between hemispheres whose respective limitations and predispositions allow for complementary capacities in processing incoming information, with the RH providing the frame within which the LH performs its more refined operations. It may be for the sake of such a cooperation that this hemispheric dissociation in terms of resolutive power has emerged during evolution" (p. 269). 12

Sergent (1987). Failures to Confirm the Spatial-Frequency Hypothesis: Fatal Blow or Healthy Complication (1987)? "While the spatial-frequency hypothesis is not entirely supported by all the existing indirect evidence, none of the findings reported so far seem to disprove it... Detection tasks have shown equal sensitivity of the two hemispheres in early visual processes (see Kitterle, 1986, for a review), and, although some authors have considered such a finding as evidence against the hypothesis (e.g., Delis, Robertson, & Efron, 1986), the hypothesis does specifically predict this outcome (Sergent, 1982a)" (p. 415). Peterzell, Harvey & Hardyck (1989). Spatial frequencies and the cerebral hemispheres: Contrast Sensitivity, visible persistence, and letter classification Experiments 1 & 2: (UC Berkeley w/ Hardyck, 1981-84) 1. Contrast Sensitivity (DeValois Lab) 2. Visible Persistence Experiment 3: (CU Boulder w/ Harvey, 1984-85) 3. Letter Classification 13

Peterzell, Harvey & Hardyck (1989). Spatial frequencies and the cerebral hemispheres: Contrast Sensitivity, visible persistence, and letter classification Experiment 1 Peterzell, Harvey & Hardyck (1989). Spatial frequencies and the cerebral hemispheres: Contrast Sensitivity, visible persistence, and letter classification Experiment 2 14

Peterzell, Harvey & Hardyck (1989). Spatial frequencies and the cerebral hemispheres: Contrast Sensitivity, visible persistence, and letter classification Experiment 3 - Sergent’s experiment with direct manipulation of spatial frequency Same letters: L, H (targets); T, F (non-targets) Alternative hypothesis? RH and “information degredation” (Michimata & Hellige) Spatial frequency: c/deg or c/object? Response Bias? 2 deg 1 deg 0.5 deg 1 2 4 8 16 c/deg 15

2 deg 1 deg 0.5 deg 1 2 4 8 16 c/deg 16

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In subsequent years… • Sergent refined her hypothesis, studied other things until ‘94 • Sergent began to emphasize the limits of computational, neuroimaging approaches to understanding the brain • Christman, Kittlerle, Hellige and others attempted to test the hypothesis in a series of experiments in the ‘90’s, and debated Peterzell • Peterzell (1998) challenges the originality, conclusions of Ivry & Robertson. 19