"Titchener circles" meaning in English

{
  "etymology_text": "The illusion was popularized in the English-speaking world by Edward B. Titchener in a 1901 psychology textbook.",
  "head_templates": [
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      "expansion": "Titchener circles pl (plural only)",
      "name": "en-noun"
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  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
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          "name": "English entries with incorrect language header",
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            "Entry maintenance"
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          "source": "w"
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        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Optical illusions",
          "orig": "en:Optical illusions",
          "parents": [
            "Vision",
            "Senses",
            "Perception",
            "Body",
            "All topics",
            "Fundamental"
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          "source": "w"
        }
      ],
      "glosses": [
        "Synonym of Ebbinghaus illusion"
      ],
      "id": "en-Titchener_circles-en-noun-JvR2q7Jl",
      "links": [
        [
          "Ebbinghaus illusion",
          "Ebbinghaus illusion#English"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "Ebbinghaus illusion"
        }
      ],
      "tags": [
        "plural",
        "plural-only"
      ]
    }
  ],
  "word": "Titchener circles"
}

{
  "etymology_text": "The illusion was popularized in the English-speaking world by Edward B. Titchener in a 1901 psychology textbook.",
  "head_templates": [
    {
      "args": {
        "1": "p"
      },
      "expansion": "Titchener circles pl (plural only)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English eponyms",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English pluralia tantum",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Optical illusions"
      ],
      "glosses": [
        "Synonym of Ebbinghaus illusion"
      ],
      "links": [
        [
          "Ebbinghaus illusion",
          "Ebbinghaus illusion#English"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
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          "word": "Ebbinghaus illusion"
        }
      ],
      "tags": [
        "plural",
        "plural-only"
      ]
    }
  ],
  "word": "Titchener circles"
}